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DEEL 116 4 1973

TIJDSCHRIFT

VOOR ENTOMOLOGIE

UITGEGEVEN DOOR

DE NEDERLANDSE ENTOMOLOGISCHE VERENIGING

DEEL 116 anand i 1973

TIJDSCHRIFT

VOOR ENTOMOLOGIE

UITGEGEVEN DOOR

DE NEDERLANDSE ENTOMOLOGISCHE VERENIGING

Tijdschrift voor Entomologie, deel 116, 1973

Afleveringen 1, 2, 3, 4 zijn verschenen 1 februari 1973

Afleveringen 5, 6, 7 zijn verschenen 27 juni 1973

Afleveringen 8, 9, 10 zijn verschenen 19 oktober 1973

Afleveringen 11, 12 13 zijn verschenen 31 december 1973

Aflevering 14 is verschenen 18 februari 1974

INHOUD VAN DEEL 116

ALLEMAN, H., zie Hollander, J. den, etc.

DIJKSTRA, H., zie Hollander, J. den, etc.

FAIN, A., zie Lukoschus, F. S.

FOKKINGA, A., zie Kessler, A.

Gaur, J., W. RAMIREZ B. & D. EISIKOWITCH. — Pollination of Ficus costaricana

and F. hemsleyana by Blastophaga esterae and B. tonduzi in Costa Rica (Hy-

menoptera: Chalcidoidea, Agaonidae) I ER

HOLLANDER, J. DEN, H. Dijkstra, H. ALLEMAN & L. VLIJM. — Courtship

behaviour as species barrier in the Pardosa pullata group (Araneae, Lycosidae)

Kasy, F. — Beitrag zur Kenntnis der Familie Stathmopodidae en 1913.

(Lepidoptera, Gelechioidea)

KESSLER, A. — A comparative study of the production of eggs in eight Pardosa

species in the field (Araneae, Lycosidae) DA ARE,

KESSLER, A. & A. FOKKINGA. — Hymenopterous parasites in egg sacs of spiders of

the genus Pardosa (Araneae, Lycosidae) DT

KUMANSKI, K. — Die Unterfamilie Drusinae (Trichoptera) in Bulgarien

LANSBURY, I. — A review of the genus Cercotmetus Amyot & Serville, 1843

(Hemiptera-Heteroptera: Nepidae)

LITH, J. P. van. — Psenini from Nepal (Hymenoptera, Sphecidae)

LukoscHus F. S., P. G. ROSMALEN & A. FAIN. — Parasitic mites of Surinam. —

XI. Four new species of the genus Psorergatoides Fain, 1939 (Psorergatidae:

Trombidiformes) AO SOR

PETERICH, L. — Chromatologie, eine Untersuchung der Chromatik der Fauna und

Flora auf deren rein-chromatische Gesetzlichkeiten

ROSMALEN, P. G., zie Lukoschus, F. S.

SCHMID, F. — A propos d’hybridisme naturel chez les Be ous

Papilionidae) A : Se : SE

THOMSON, G. — Geographical variation of Maniola jurtina (L.) (Lepidoptera,

Satyridae) Seni I WET I a ae SN Le An

VLIJM, L., zie Hollander, J. den, etc.

Worrr, N. L. — Notes on Pammene ignorata Kuznetsov, 1968 Ae ae

Tortricidae) MRC Pee o 5

Alphabetical index

Corrigenda. .

227,

107

123

143

185

301

302

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YS. COMP. zoo OL:

à LIBRARY

n° APR 6 1973

4 TIJDSCHRIFT

| VOOR ENTOMOLOGIE

UITGEGEVEN DOOR

398 DE NEDERLANDSE ENTOMOLOGISCHE VERENIGING

INHOUD

u KJ: DEN HOLLANDER, H. DIJKSTRA, H. ALLEMAN and L. VLIJM. — Courtship behaviour as

| species barrier in the Pardosa Pullata group (Araneae, Lycosidae), p. 1—22.

Gepubliceerd 1-11-1973

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amine ee

tt eh air re pr kite ta

COURTSHIP BEHAVIOUR AS SPECIES BARRIER IN THE

PARDOSA PULLATA GROUP (ARANEAE, LYCOSIDAE)

J. DEN HOLLANDER, H. DIJKSTRA, H. ALLEMAN AND L. VLIJM

Department of Biology, Free University, Amsterdam

ABSTRACT

The composition of the behaviour of males of three species of the Pardosa pullata group —

P. prativaga (L. Koch), P. sphagnicola (Dahl) and P. pullata (Clerck) — is described, depending

on both conspecific and non-conspecific stimuli.

The isolating mechanisms between the species studied are investigated in interbreeding experiments.

The relative importance of behaviour as species barrier in the Pardosa pullata group is discussed.

CONTENTS

I. Introduction 2

II. Materials and methods 2

a. Materials 2

b. Methods 3

c. The behaviour Sii Der 0 died 4

III. Results ; 5

A. Confrontation cio 5

1. Recordings of behaviour 5

1.1. Frequencies and durations of the recorded Peau elements 5

1. P. prativaga . 6

2. P. sphagnicola 7

3. P. pullata 8

4. Conclusions . 8

1.2. Sequences of the recorded behaviour elements . 9

1. P. prativaga . 11

2. P. sphagnicola 11

3. P. pullata 11

4. Conclusions . 14

2. Influence of the respective stimulus situations . 14

2.1. Total numbers of activies . 14

1. P. prativaga . 14

2. P. sphagnicola 14

3. P. pullata 14

4. Conclusions . 14

2.2. Relative frequencies of the recorded behaviour elements 15

1. P. prativaga . 15

2. P. sphagnicola 16

3. P. pullata 16

4. Conclusions . 16

3. Conclusions of the confrontation Greche 17

2 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 1, 1973

B. Breeding experiments . : : 7 I à : a : : , : 17

1. Mating and egg sac construction . A : i : : A 7 : 17

2. Emergence of pulli . 5 : : . = : . ; i 18

3. Breeding of pulli x ; À : : : 3 . 5 : : 18

4. Conclusions 3 ; 3 : : : : 8 . 3 : 3 18

IV. General conclusions and discussion . à : ; E : : 2 : 19

1. General conclusions . A : : 4 A . . à 19

2. Discussion with regard to behaviour composition . à : : : 19

3. Discussion with regard to interbreeding . : 4 3 : : 20

4. Discussion with regard to isolating mechanisms : 7 ; o 21

V. Summary : 5 2 : : - x : 7 ; : ; 7 d 21

VI. Acknowledgements . : ; : ; . È : 3 3 : 3 : 22

VII. References : 3 : : : : : : : : ; : : E 22

I. INTRODUCTION

The Pardosa pullata group is constituted of a number of closely related species, in

morphological (Wiebes, 1959; Holm and Kronestedt, 1970; Den Hollander, 1970), as

well as in ecological respect (Richter et al., 1971; Den Hollander, 1971; Den Hollander

& Lof, 1972). As morphologically intermediate specimens have been found, the pos-

sibility of the occurrence of interbreeding in the field has been suggested (Locket &

Millidge, 1951; Den Hollander, 1970). Under natural conditions several mechanisms

may operate to prevent interbreeding (Mayr, 1969). Concerning species of the Pardosa

pullata group Den Hollander (1971) and Den Hollander & Lof (1972) studied seasonal

and habitat factors acting as barriers against interbreeding. They found that such factors

do not completely isolate the species studied. Otherwise, mating behaviour as well as

post-mating mechanisms may be important too in isolating the species of the P. pullata

group.

It should be mentioned that, within the genus Pardosa, courtship display is very

specific, and is therefore considered to act as an important barrier between the species

(Bristowe & Locket, 1926). Ethological isolating mechanisms, i.e. bartiers to mating due

to incompatibilities in behaviour, represent the largest and most important class of

isolating mechanisms in animals (Mayr, 1969). As a consequence of the biological

species concept (Mayr, 1940) isolating mechanisms “are perhaps the most important

set of attributes a species has, because they are, by definition, the species criteria” (Mayr,

1969).

The present paper mainly deals with courtship behaviour of the species of the

Pardosa pullata group in the context of the importance of behaviour as an isolating

mechanism. Besides, some observations on the occurrence of mechanical and post-mating

isolating mechanisms between the species studied are dealt with.

II. MATERIALS AND METHODS

IIa. Materials

The study was carried out with three species of the P. pullata group, viz., Pardosa

prativaga (L. Koch, 1870), P. pullata (Clerck, 1757) and P. sphagnicola (Dahl, 1908),

which species normally occur in the Netherlands (Den Hollander, 1970; P. prativaga

DEN HOLLANDER, DIJKSTRA, ALLEMAN & VLIJM: Courtship behaviour in Pardosa 3

var. fulvipes (Collett, 1875) stands for P. sphagnicola). Subadult specimens were col-

lected from several populations in the Netherlands and France (Table 1). They were

kept at low temperature, about 5° C. Before the experiments started, the spiders were

transferred to room temperature. After a few days the final moult then occurred. During

the experiments temperature ranged from 28-30° C and the relative humidity from

70 to 90%.

IIb. Methods

A. Confrontation experiments.

In these experiments each male was observed individually under various stimulus

situations (Table 2). Males were tested on conspecific as well as non-conspecific sub-

strates, both in the absence (5, resp. 1 and 3) and presence of females, being either

conspecific (8, resp. 9 and 10) or non-conspecific ones (6 and 7, resp. 2 and 4) (the

figures indicate the codes of the respective stimulus situations (Table 2).

The behavioral data were recorded with the help of a 20 channel event recorder

Table 1. The localities of the populations of the Pardosa pullata group used in the present study

(cf. Den Hollander, 1971; Den Hollander et al., 1972)

Locality Species Experiment

The Netherlands

Vogelenzang, Heemstede pra A and B spring, resp. autumn

Hollandse Rading, Hilversum pul A and B spring, resp. autumn

Bosweitje, Rockanje pra, pul B spring

De Eese, Steenwijk sph A and B spring, resp. autumn

Woldberg, Steenwijk sph B spring

France

Selon, Hérault pra B spring

Palavas, Hérault pra B spring

Etang de Brion, Yonne pra B spring

Le Pin, Yonne pra, pul B spring

(Esterline - Angus) wired to two 10-key keybords. A paper speed of 50 cm/min was

used. In this way the preservation of records on frequencies and durations as well as

the temporal patterning of behaviour elements was made possible. The occurrence of

a behaviour event was recorded by depressing the appropriate key for the duration of

that behaviour. It is evident that the accuracy of establishing durations of less than about

two secs. will be small.

Three males and three females of each species were used in these experiments. In

the stimulus situations 5 and 8 (Table 2) each male was tested. In the other experiments

the observations were carried out with individuals which were chosen at random out of

the three males and three females.

B. Breeding experiments.

In these experiments 4-6 males were put in glass boxes together with the same

number of females of the different species (non-conspecific females). One or two

conspecific females were added. In these experiments the occurrence of mating and

afterwards, construction and carrying of egg sacs by the females, as well as the devel-

4 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 1, 1973

opment of the eggs in the egg sacs and the development of the pulli emerging from

the egg sacs, were recorded.

Table 2. The respective stimulus situations in which the behaviour of the males of the species

studied was recorded; pra = prativaga, pul = pullata, sph = sphagnicola

Code Number of Pardosa prativaga Pardosa sphagnicola Pardosa pullata

experiments males males males

substrates females substrates females substrates females

(S 2) (CR CE) (2) 69) (2)

1. 2 sph — pra — pra —

2. 2 sph sph pra pra pra pra

3: 2 pul — pul — sph —

4. 2 pul pul pul pul sph sph

5: 8 pra — sph — pul —

6. 2 pra sph sph pra pul pra

Te 2 pra pul sph pul pul sph

8. 12 pra pra sph sph pul pul

9. 2 sph pra pra sph pra pul

10. 2 pul pra pul sph sph pul

IIc. The behaviour of the species studied

Courtship behaviour of Lycosid spiders was studied thoroughly by Vlijm and co-

workers (Vlijm & Dijkstra, 1966; Vlijm & Borsje, 1969; Dijkstra, 1969; Vlijm, Den

Hollander & Wendelaar Bonga, 1970; Dijkstra, Van der Ploeg & Koomans, in prep.).

In these studies courtship behaviour is considered to be that kind of behaviour of the

males which especially occurs in the presence of females of the same species.

Up till now little work has been done on the behaviour of species of the P. pullata

group. Hallander (1967) stated that P. pullata does not show any courtship display

and that the male directly jumps on the female to mate. However, Vlijm & Borsje (1969)

observed specific movements of palps and legs as well as a special way of locomotion

in the precopulatory phase of this species. Consequently these authors concluded that

above mentioned behavioral elements may by considered courtship behaviour.

P. prativaga and P. sphagnicola, on the other hand, show a very distinct courtship

display consisting of palpal movements comparable with those described for the Pardosa

amentata group (Vlijm & Dijkstra, 1966), as well as special patterns of locomotion

(unpublished results, e.g., film records, from the laboratory).

With the help of the following list of elements, the behaviour of males of the

species studied could be satisfactorily described in the respective stimulus situations,

A. Locomotory behaviour, non-oriented at female :

Walking (W) : normal locomotory activity.

Jerky walking (Jw) (Dijkstra, 1969) : jerky locomotion; described as “Hopping” for

P. pullata by Vlijm & Borsje (1969).

Searching (S) (Vlijm & Borsje, 1969) : slow continuous locomotion in which the body

is near to the substrate and the palps are continuously in contact with the substrate.

DEN HOLLANDER, DIJKSTRA, ALLEMAN & VLIJM: Courtship behaviour in Pardosa 5

Searching walk (Sw) : Jerky locomotion with the body near to the substrate and the

palps drumming on it.

Stalking (St) (Dijkstra, 1969) : slow locomotion in which the legs are moved very

stealthily.

B. Locomotory behaviour, oriented at female :

Encircling (E) (Dijkstra, 1969) : after touching the female the male retreats and moves

in a semi-circle around the female, his front remaining directed towards the female

throughout.

Hopping (H) : first the body, and especially the abdomen, is raised, the legs being wide

apart. Then, in a sudden movement (“hop”), the body is lowered between the legs,

quivering violently. After this the male takes a step in the direction of the female.

Copulation attempt (Ca) : the male jerkily runs up to the female, lowering the abdomen

to the substrate, stretching the front legs to touch the female, and tries to mount the

female.

C. Oscillatory movements of abdomen and palps :

Abdomen vibrating (Av) (Vlijm & Dijkstra, 1966) : the tip of the abdomen violently

quivers up and down, sometimes touching the substrate.

Palp vibrating (Pv) (Vlijm & Dijkstra, 1966) : both palps simultaneously move

quickly up and down, while kept in their normal curved position.

Palp cycling (Pc) : the palps are, alternately, stretched and raised after which they are

lowered and brought back to their normal, curved, position.

D. Single movements of legs and palps :

Leg waving (Lw) (Dijkstra, Van der Ploeg & Koomans, in prep.) : slow motions of

the legs of first pair. They are stretched and raised and then brought back to their

testing position. The tips of the legs describe an arch in this way.

Palp waving (Pw) (litt. see Leg waving) : the same motions of the palps as described

for the front legs under “Leg waving”. Vlijm & Borsje (1969) described Leg and

Palp waving as “courting”.

Leg beating (Lb) : one of the front legs is stretched and moved up and down rather

quickly.

E. Other behaviour elements :

Spinning : (Sp) (Richter, 1970) : production and attachment of silk.

Preening (P) (Vlijm & Borsje, 1969) : drawing a leg or a palp through the chelicerae.

Rubbing (R) : rubbing two adjacent legs together; synonymous with Double preening

(Vlijm & Borsje 1969).

Some of these behaviour elements occurred throughout the species studied, while

others appeared to be restricted to one or two of the species only. Besides, comparable

behavioral components do vary in structure between the respective species. This variation,

however, will not be described in this paper.

III. RESULTS

A. Confrontation experiments

A 1. Recordings of behaviour

A. 1.1. Frequencies and durations of the recorded behaviour elements.

Males of the species studied were tested in two stimulus situations, viz. conspecific

6 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 1, 1973

substrates, either without or with conspecific females (Table 2, situations 5 and 8,

respectively), The experiments lasted 20 min. or, when mating occurred, till the moment

of mating. In total eight experiments per species were performed on substrate only

(sit. 5) and twelve with females present (sit. 8). The results are presented in Table 3.

1.1.1. P. prativaga:

In the stimulus situation S ® (pra) males spend most of the period of activities (total

duration) in Jerky walking, Palp cycling, Preening and Walking together (more than)

90%). Concerning Preening and to a lesser extent, Walking, this is due to the rather

long duration of each period of Preening and Walking, respectively. On the other hand,

the periods of Jerky walking as well as Palp cycling last much shorter. However, their

frequencies are high, Thus these two activities also to a large extent contribute to

the total period of activities.

In the stimulus situation SQ (pra) + Q (pra) some differences occur as compared

with SQ (pra). The level of activity, i.e. the total duration of the recorded activities, is

lower in the situation SQ + 9 (604) than in SQ (860). In the stimulus situation

SQ + 9, males spend up to one third of the total period of activities in Abdomen

and Palp vibrating, Hopping, Encircling and Copulation attempt together, at the cost

of the remaining behaviour elements. Nevertheless Preening, Walking, Jerky walking

and Palp cycling together still take up to 60% of the total period of activities.

The set of behaviour elements Abdomen and Palp vibrating, Hopping, Encircling and

Table 3. Frequencies and durations of recorded behaviour

Pardosa prativaga

Behaviour total frequency mean range of total

element duration duration mean dur. duration

(sec) (sec) per exp. (sec)

Preening 202 70 11 5 18.4 13.6 8.2—30.0 158 33

Walking 96 40 14 7.67) MSS DAS 0 46 21

Rubbing 16 5 6 RE 235 1.6— 4.8 25 15

Spinning 7 5 6 sio UD 70-12 6 3

Jerky walking 299 135 105 43 2.9 3.1 1.3— 7.0 25 11

Searching 10 17 3 7. 3.1 2.6 1.6— 4.8 126 48

Searching walk 24 11 9 4 2.8 3.7 1.2— 4.8 19 4

Palp cycling 204 121 114 59 1.8 2.0 1.4— 2.4 55 13

Copulation attempt — 23 — 15 1.5 0.8— 2.6 — 2

Encircling = 13 — 9 1.4 1.0— 3.6 — ._

Abdomen vibrating 2 91 1 40 12 2.3 1.2— 4.9 14 318

Palp vibrating — 50 — 24 251 1.7— 2.9 5 252

Hopping -- 23 — 10 2.3 1.2— 4.8 — 107

Leg beating — — — — 66 14

Leg waving — — — — 16 2

Palp waving — — — — 1 —

Stalking — — — — — —

Total duration 860 604 | 562 843

Situation (Table 2) 5 gis gd 8 548 mals 8

DEN HOLLANDER, DIJKSTRA, ALLEMAN & VLIJM: Courtship behaviour in Pardosa 7

Copulation attempt only occurs in the stimulus situation SQ + 9. These activities thus

may be considered Courtship Display. The durations of the respective elements of

Courtship Display are rather short and of the same length throughout. Particularly

Abdomen and Palp vibrating show high frequency values as compared with other

elements in the behaviour of P. prativaga males.

In both stimulus situations the frequencies as well as the durations of Rubbing,

Spinning, Searching and Searching walk are rather small. Leg beating, Leg waving,

Palp waving as well as Stalking do not occur at all in the behaviour of P. prativaga

males.

1.1.2. P. sphagnicola :

In the stimulus situation SQ (sph) up till 80% of the total period of activities

consisted of Preening, Searching, Leg beating, Palp cycling and Walking together. As in

P. prativaga, the mean durations of Preening and Walking are rather high. In Pardosa

sphagnicola the same holds for Searching. None of the recorded elements in the

behaviour of P. sphagnicola males shows, as extremely high frequencies, as occur in

Pardosa prativaga (Jerky walking, Palp cycling).

Under the stimulus situations SQ (sph) + @ (sph) the behaviour of P. sphagnicola

males changes considerably as compared to SQ (sph). The total duration of the recorded

activities increases from 562 to 843 secs. 80% of this period is spent in Adomen and

elements of males in the stimulus situations 5 and 8 of Table 2

Pardosa sphagnicola Pardosa pullata

frequency mean range of total frequency main range of

duration mean dur. duration duration mean dur.

(sec) per exp. (sec) (sec) per exp.

74 2 24.0 17.2 1.2—40.8 175 101 9 5) 20.3 22.0 7.2—36.0

8 4 5.5 5.0 1297 63 37 8 U 8.1 Zeil 1.2—13.3

5 3 4.7 4.2 1.8— 7.2 12 10 3 3 3.8 4.3 1.8— 6.0

5 2 1.1 1.2 0.8— 1.8 3 1 2 1 123 1.3 1.2— 3.5

6 4 4.0 3.1 1.2— 7.2 25 33 4 6 6.6 8.2 1.2—10.1

14 6 9.2 8.3 1.2— 26.4 99 82 8 8 12.6 10.5 3.1—34.2

7 1 2.9 3.0 1.2— 4.8 128 122 13 9 9.6 13.4 1.2 31.7

16 5 3.5 2.6 1.2— 10.4 3 1 2 2 1.7 0.3 0.5— 2.4

= 2 1.2 1.2—18.6 — 1 3 1.6 1.2— 2.8

2 41 6.5 7/55) 2.4—21.6 — — — —

if 42 37. 5.3 1.2— 19.6 — — — —

a 36 1.2 1.9— 7.2 — —

13 5 4.9 3.2 1.0—12.7 39 24 7 5 5.9 527. 1.2—24.0

6 1 2.6 27 1.2— 7.7 1 11 1 4 1.3 2.8 1.2— 6.6

1 — 1.0 1.1— 1.8 — 3 — 2 1135) 1.2— 14

— — — 4 — 1 4.0 1.7— 9.0

| 548 433

5 gr WS 8 Ss 5 ren 8 5+8

8 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 1, 1973

Palp vibrating and Hopping, while the period spent in each of the remaining behaviour

elements decreases.

Abdomen and Palp vibrating as well as Hopping especially occur in the situation

SQ + 9 as compared with the situation SQ. Thus this set of behaviour components

may be considered Courtship Display. All elements of Courtship Display show rather

high frequencies as compared with the other behaviour elements. When compared to

P. prativaga the mean durations of Abdomen and Palp vibrating are much higher in

P. sphagnicola, that of Hopping being of the same length. Both Copulation attempt and

Encircling hardly occur in the behaviour of P. sphagnicola males.

In both stimulus situations the frequencies and durations of Rubbing, Spinning, Jerky

walking, Searching walk, Leg and Palp waving are small, whereas Stalking does not occur

at all. Thus, major differences between P. sphagnicola and P. prativaga are found in

Courtship Display, Leg beating, Searching and Jerky walking.

1.1.3. P. pullata:

In both stimulus situations (SQ (pul); SQ (pul) + 2 (pul)) Preening, Searching

walk, Searching and Walking together take up to 80% of the total period of activities.

The mean durations of all these behaviour elements are rather long, The same holds

for Jerky walking, however, the frequency of this element is low, and therefore it

contributes only to a small extent to the total period of activities. As in P. sphagnicola,

none of the recorded activities show extremely high frequencies.

The situations in which conspecific females are present on the substrate (SP (pul)

+ © (pul)) the behaviour of P. pullata males does not change much. The level of

activity is of the same height in both stimulus situations; so are the frequencies and total

durations of most of the recorded elements. Copulation attempt, Leg and Palp waving

as well as Stalking only or especially occur in the stimulus situation SQ (pul) + 9

(pul). Although their frequencies and total durations are very small, this set of elements

may be considered Courtship Display.

Rubbing, Spinning, and Palp cycling hardly occur in the behaviour of P. pullata

males. Encircling, Abdomen and Palp vibrating as well as Hopping, elements of Court-

ship Display in both other species, do not occur in P. pullata. On the other hand,

Courtship Display in P. pullata consists of elements which do not occur in P. prativaga

and hardly in P. sphagnicola. However, P. pullata males spend only 5% of the total

period on these activities.

In the species studied the mean duration of each behaviour element varies to a large

extent, both between the respective experiments per species and within experiments.

Thus, e.g., the mean duration of Preening varies between the respective experiments

from 1.2 to 40.8 sec. (Table 3 : range of mean durations per experiment in Pardosa

sphagnicola). Within the experiments the duration of Preening may vary from 1 up to

150 sec. Differences between the respective situations are small throughout the species

studied, with respect to both types of variation.

1.1.4. Conclusions :

In the three species studied Preening and Walking take an important part in the

behaviour of the males as the mean durations of these elements are long, though their

frequencies are of moderate value. Rubbing and Spinning scarcely occur in the behaviour

of the males studied.

DEN HOLLANDER, DIJKSTRA, ALLEMAN & VLIJM: Courtship behaviour in Pardosa 9

Differences between the species studied occur in the elements of Courtship Display

as well as in Palp cycling, Jerky walking, Searching, Searching walk and Leg beating,

both in frequencies and durations. Palp cycling and Jerky walking occur in high fre-

quencies in P. prativaga. P. sphagnicola and P. pullata spend considerable periods in

Searching, as the mean duration of this element is high, Both frequency and mean

duration of Searching walk is higher in P. pullata, as compared with both other species.

Leg beating does not occur in P. prativaga.

In P. sphagnicola Courtship Display takes most of the time spent by the males;

P. pullata males spend only a very small part of time in Courtship Display. Courtship

Display is rather similar in P. prativaga and P. sphagnicola. The elements of this

behaviour do not occur in P. pullata, on the other hand elements occurring in Courtship

Display of P. pullata hardly occur in P. sphagnicola and P. prativaga.

A. 1.2. The sequences of the recorded behaviour elements.

The frequencies of any of two given elements i and j in the behaviour define the

number of successions of both elements, provided they are randomly distributed in that

behaviour. The chance that element i occurs is put down in formula as e; = n;/N, in

which n; represents the frequency of element i, and N the total number of activities

(sum of the frequencies of all occurring elements). In the same way e; = n;/N. The

chance that both elements occur together e,,, = n;.n;/N2. The number of successions

of the elements i and j will amount to e,,.N = n;.n;/N.

In the case that the elements i and j are not randomly distributed in the behaviour,

i.e., when they are arranged in a pattern, the observed number of successions n;,; 7

n.n,/N.

So sequence analysis means that the observed number of successions of any pair of

elements i and j (n;,;) will be compared with the expected number of successions of

both elements when they were randomly distributed in the behaviour (e;,;.N) (chi-square

test, one degree of freedom, a = 0.01). Behaviour patterns can be performed with the

help of those successions which observed numbers exceed the expected ones.

Regarding the results, two points should be taken into account. First, only changes

in behaviour have been taken into consideration. So repetition of elements has not been

recorded. Second, immobility, though not being behaviour, has been inserted in the

sequence diagrams because preliminary observations showed that switches in behaviour

(e.g. from Walking to Courtship Behaviour) often are mediated by a period of

immobility (Dijkstra, 1969). Immobility is defined as those periods of at least five

seconds during which the observed spider did not show overt behaviour.

Behaviour patterns have been established for three stimulus situations, viz, non-

conspecific substrates, and conspecific substrates, either without or with conspecific

females (Table 2: 1 + 3, 5, 8 respectively). The observed numbers of successions of

each pair of behaviour elements have been summarized irrespective of the length of the

observation period. Four experiments were carried out in the stimulus situation SQ

(non-conspecific). The total observation period of both P. prativaga (S © (sph) +

S © (pull)) and P. sphagnicola (S 9 (pra) + S 9 (pull)) amounted to 80 min,

that of P. pullata (S Q (sph) + S 9 (pra)) to 60 min. In the stimulus situation

S ® (conspecific) eight experiments were carried out, each lasting for 20 min., with

each of the species studied. Twelve experiments were performed in the situation S 9

+ ® (both conspecific). In both P. prativaga and P. pullata the length of the ob-

19 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 1, 1973

I.S9 (Sph)+ SP (pul) S

t.n.a. 502 40

[26

onp man "= |

128 58 56 1027750777 1407287 022

P-I->R

37 10

I.Sg£ (pra) S

t.n.a. 2265 33

Ww = 1-59, uw 226 Po 50 sw

111 16 101 848 668 908 58 73

| 26

85 12 43

II.Sg (pra)+ ® (pra)

t.n.a. 1519

_28 _

I va

7 3

126 84 211 83

slo 39 =D

yee 308. Ir

Ww 11. FEN Jw Zoe. U (ey

47 127 296 169 350 28 33

LE EEE (so

17 Vases

50% 8 101016

Fig. 1. The behaviour patterns of males of P. prativaga studied in three different stimulus situations

(Cf. also caption of Fig. 3)

DEN HOLLANDER, DIJKSTRA, ALLEMAN & VLIJM: Courtship behaviour in Pardosa 11

servation period varied from 2.5 to 20 min. per experiment, in P. sphagnicola each

experiment lasted 20 min. Thus the total observation period of P. sphagnicola males

amounted to 240 min., that of P. prativaga males to 120 min., and that of P. pullata

ones, to 134.5 min.

The aim of these experiments is to establish the specific events of behaviour of the

respective species. Therefore a comparison is made between the behaviour patterns in the

situations non-conspecific substrates (less-specific situations) (Table 2; 1, 3), con-

specific substrates (5) and conspecific substrates together with conspecific females (more

specific situations) (8).

Figs. 1, 2 and 3 present the behaviour patterns of the respective species.

1.2.1. P. prativaga (Fig. 1).

In both stimulus situations without females the behaviour of P. prativaga males consists

of a well patterned series of elements. Palp cycling takes a central position; it follows

Searching, Searching walk, as well as Jerky walking. Palp cycling is followed by Searching

walk and Jerky walking again, and Preening.

In the presence of females (S @ (pra) + © (pra)) this pattern is mainly the same.

Major differences concern the relation between Jerky walking and Walking and, naturally,

Courtship Display. Jerky walking and Walking alternate in the latter pattern whereas

they are not related at all in the former. Courtship Display is connected with the former

pattern mainly through Abdomen vibrating and Immobility, The pattern of Courtship

Display exists of alternating Abdomen and Palp vibrating, followed by Hopping.

Hopping ends in Copulation attempt, which, when mounting does not succeed, is

followed by Abdomen vibrating again, either directly or via Encircling. The cycle may

then start again. Courtship Display ends, if not in mating, through both above mentioned

elements in either Immobility or Palp cycling.

1.2.2. P. sphagnicola (Fig. 2).

In contradistinction to P. prativaga, the elements of behaviour in P. sphagnicola

are arranged in a cyclic pattern under conditions where males are studied on non-con-

specific substrates. Besides this cyclic pattern the elements Searching and Leg waving

take a distinct position.

The behaviour pattern of P. sphagnicola males clearly consists of two parts in the

stimulus situation SQ (sph), one set of elements arranged around Immobility, another

around Searching.

In the presence of females (SQ (sph) + @ (sph)) the males of P. sphagnicola are

mainly engaged with Courtship Display. Under these conditions the frequencies of all

other elements decrease in such a way that it is impossible to establish any relations

with good confidence. Courtship Display starts through Immobility, as in P. prativaga.

It mainly consists of both Abdomen and Palp vibrating followed by Hopping and vice

versa. In some cases Hopping leads to Copulation attempt, and, when this fails Abdomen

and Palp vibrating starts again. Courtship Display ends, if not in mating, through

Abdomen vibrating in Immobility.

1.2.3. P. pullata (Fig. 3).

As in P. prativaga the behaviour of P. pullata males has been patterned in a series in

the stimulus situation SQ (sph) + S? (pra), though other elements are involved than

12 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 1, 1973

TS? (pra)+ Ss (pul)

t.n.a. 455

_- SW

1024 927 11

7 “> 13 5

11 59 102 SZ Lw

12 OS OR 36

10 17 Pc

dw spre

44 22

IT Sg (sph)

t.n.a. 950

15 1

Van 42

a 47 re

Po = 5 20 lw

\e 23 135 42 147 20 61

Jw 22 6

49 m

LD) Sp

117 50

II S$ (sph)+ 2 (sph)

tma 2485

20 zo 20

Pv = 3740 H - 406 7 Av Pc

486 404 “ 797 3747 529 59 «

53 Is PENNE

34 EN

Wiesen on 4,

48° 26 182 19 292 24

I 5 IR

14,7 i 50

LA Wage

Jw Lb

46 54

Fig. 2. The behaviour patterns of males of P. Sphagnicola studied in three different stimulus

situations. (Cf. also caption of Fig. 3)

DEN HOLLANDER, DIJKSTRA, ALLEMAN & VLIJM: Courtship behaviour in Pardosa 13

I sg (sph)+S? (pra)

t.n.a. 310

FE PRE Sorg SO dio ya yy

37 55 66 47 40 23

Son (pul)

nia 578

115

18 v 13

48 15 74 56 14 58

47.

pe SW

IMI S$ (pul)+ 9 (pul)

t.n.a. 467 10

P------ > R

32 21

S 16 > SW < 24 I . 15 W

53 61 101 34

Fig. 3. The behaviour patterns of males of P. pullata studied in three different stimulus

situations. Broken lines indicate successions showing high chi-square values, from which, however,

the expected frequencies amounted to less than five, i.e., the total frequencies of either or both

elements are too low for confident testing with the chi-square method. The figures on the arrows

indicate the observed numbers of successions; figures below the element codes represent the

frequencies of these elements. t.n.a.: the total numbers of activities.

in the former species. In the stimulus situation S 9 (pul) this series is split up into three

pairs of alternating elements, viz. Immobility and Searching walk, Walking and Preening,

Searching and Leg beating. However, Preening and Searching are also related to each

other in that the former element follows the latter.

In the presence of females (SQ (pul) + @ (pul)) the pattern again changes,

consisting mainly of the arrangement of Leg waving, Walking and Searching walk

14 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 1, 1973

around Immobility. Courtship Display hardly occurs in this species, so it was not possible

to establish the pattern of this component of behaviour with good confidence. However,

as Leg waving, which is the major constituent of Courtship Display, follows on Im-

mobility, it may be concluded that, as in the two other species, Courtship Display is

connected with the remaining behavioral elements through Immobility.

1.2.4. Conclusions.

These results show that the behaviour patterns are rather specific. Similarities hardly

occur between the patterns of the three species, in comparable situations. Rather strict

relations occur between Rubbing and Preening in each of the species, but the frequencies

of both elements are low.

Major differences in pattern between the species studied concern the arrangement of

the elements Immobility, Walking and Jerky walking (P. prativaga and P. sphagnicola

contra P. pullata), as well as the strict relation between the elements Palp cycling and

Jerky walking (P. prativaga contra P. sphagnicola and P. pullata).

A. 2. Influence of the respective stimulus situations

A. 2.1. Total numbers of activities dependent on the respective external stimuli.

Table 4 presents the mean numbers of activities (= any occurrence of a behaviour

element) per male per 20 min. in the respective stimulus situations. P. prativaga males

appear to be the most active, P. pullata the least active.

2.1.1. P. prativaga.

The highest numbers of activities occur on conspecific substrates (situations 5, 6, 7, 8).

Addition of females, irrespective whether they are conspecific (9, 10) or non-conspecific

(2, 4) to non-conspecific substrates (1, 3) increases the numbers of activities of the

tested males.

2.1.2. P. sphagnicola.

The presence of conspecific females (8, 9, 10) shows the highest numbers of activities

of males as compared to the other situations. Neither conspecific substrates (5), in com-

parison to non-conspecific ones (1, 3) nor the addition of non-conspecific females to

either conspecific (6, 7) or non-conspecific substrates (2, 4) influence the numbers of

activities. An exception is only found in P. prativaga females in the stimulus situation

SQ (sph) + © (pra) as compared to situation SQ (sph).

DIS NP DA

The influences of the respective stimuli on the numbers of activities in the behaviour

of P. pullata males are rather small.

2.1.4. Conclusions.

The total numbers of activities of males of P. prativaga under the conditions of

investigation are elicited in the same way by conspecific substrates and the presence of

females on non-conspecific substrates. The numbers of activities in the behaviour of

P. sphagnicola males only increase by the presence of conspecific females, whereas they

do not seem to be affected at all in P. pullata.

DEN HOLLANDER, DIJKSTRA, ALLEMAN & VLIJM: Courtship behaviour in Pardosa 15

Table 4. The total numbers of activities per male per 20 min. and the percentual deal of particular

elements to these numbers in the respective stimulus situations for the species studied

Stimulus Relative frequencies of behaviour elements mean number

situation PW. Jw Pers Swi Ca E Av Pv. H Lb. Lw Pw. of activities

per 20 min.

S 1. sph — 12 172602076108 — 1—- — — — — 211 I

S 2. sph sph 5 5 31 36 14 2 2 — 1 — — — — — 60 N

Su Bulle 10 13, 13 26 10 20 — TnT — 110 2

~ 4. pul pul 7 7 22 36 11 14 — — 1 — — —— — 26000

à 5. pra — BG AO AD AMEN a 250 MRS:

Ÿ 6. pra sph BER eos 4 iy Delle

S 7. pra pul LIO AO AO ANS OU RE 230) 0,8

o» 8. pra pra Dan 3 2042205530 2° Tre 18 Se a 138 os

9. sph pra ZUSENDEN ZZ LA 329, II n 190

10. pul pra ek ARTIST NN A 107 » 97297 99 ee = 76

S 1. pra — 12 24 10 4 17 12 — — 1 — 13 6 — 82 I

S 2. pra pra OMNIA STD 62200015 Rn... 2 87 N

S 3. pul — 10 15 11 10 20 3 — — 1 — —27 — — 42 S

> 5. sph — SE TON MON) UN 1a 10) 8 — 141 N

& 6. sph pra Se Sues, RI 13, Ge = 74 LSO 57 3 — 72 oS

S 7. sph pul ONES Ne Leo She SA;

Ÿ 8. sph sph I DAR ANRT 8272027418237, 3 NUE na 119 Ÿ

o» 9. pra sph SMART ON RS AR VONN 42358221), 17 SMS 170 os

10. pul sph DO NES TON Où Te LE 140.27 ol By 3s 43. — 72

Ÿ 1 pra — 17210 2.1 22 13 — — — — — 21 — — 57 I

SZ pra pra i 12 21 9 — 21 14 — — — — — 16 1 — 77 N

2 basa 10 21 10 1 19 23 — — — — — 12 4 1 57 S

"> 4. sph sph 17 17 5 — 20 16 — — — — — 16 1 1 57 "+

5, nl der VIN NN RE me) CO

= pdl pil VA 0 SNS 0026 e SP AE iS ip 620s

o 7. pul sph ZA O IRAN 56 ER

8. pul pul 8 10 11 4 15 17 5 — — — — 9 8 5 46

9. pra pul 18 16 11 — 14 22 — — — — — 10 9 — 34

ToWsph pul 14 24 9 — 20 11 — — — — — 9 6.— 123

A. 2.2. Relative frequencies dependent on the respective external stimuli.

Table 4 also presents the fractions of the recorded behaviour elements by which they

contribute to the total numbers of activities in the respective situations.

2.2.1. P. prativaga.

Besides influencing the total numbers of activities (2.1.1.), the respective situations

vary the relative frequencies of particular elements. Frequencies of elements of Courtship

Display increase in the presence of conspecific females, those of all other elements being

lowered. Elements of Courtship Display are almost entirely restricted to this situation.

However, conspecific substrates (SQ (pra)) also influence the frequencies of some

elements. The frequencies of Jerky walking and Palp cycling increase, those of Searching

and Searching walk decrease on specific substrates (5, 6, 7) as compared to non-

16 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 1, 1973

conspecific ones (1, 2, 3, 4). The frequencies of Preening and Walking are lowered

both on conspecific substrates (5) and in the presence of females on non-conspecific

substrates (2, 4).

P. pullata females or substrates affect the behaviour of P. prativaga males in the same

way as P. sphagnicola ones do. An exception is found in Searching walk, the frequency

of which is relatively high in the situations SQ (pul) and SQ (pul) + 2 (pul).

2.2.2. P. sphagnicola.

Also in this species the relative stimuli influence the frequencies of the respective

behaviour elements differentially. As in P. prativaga, conspecific females increase fre-

quencies of elements involved in Courtship Display, those of all other elements being

lowered, especially of Preening, Walking, Searching, Searching walk and Leg beating.

The other elements are hardly influenced by the respective situations. The same in-

fluences, though to a lesser extent, can be established in the stimulus situations SQ

(sph) + 9. Especially the influences of P. prativaga females upon the behaviour of the

males is similar to that with conspecific females. In these situations particularly the

frequencies of Walking, Searching walk and Leg beating decrease, whereas those of

Abdomen and Palp vibrating and Hopping increase.

The frequencies of Walking, Searching walk and Leg beating, decrease and

that of Palp cycling increased with conspecific substrates (5) as compared to non-

conspecific ones (1, 3). Adding non-conspecific females to non-conspecific substrates

does not influence the behaviour of P. sphagnicola males.

Thus the behaviour of P. sphagnicola males is especially influenced by the stimulus

situations SQ + @ (sph) as well as SQ (sph) + © (pra) in stimulating Courtship

Display. The frequencies of the remaining behavioral activities are decreased in these

situations.

2.2.3. P. pullata.

The tested stimulus situations have a small influence on the relative frequencies of

particular behaviour elements of P. pullata males, as was the case with the total numbers

of activities (ch. 24.3).

Independent of the nature of the substrates, conspecific females (8, 9, 10) only affect

the frequencies of Leg beating (decreasing) and Leg waving (increasing). More elements

are involved in the situation SQ (pul) + © (pul): the frequencies of Palp waving

and Copulation attempt increase whereas those of Walking and Preening decrease (8). |

Conspecific substrates (5, 6, 7, 8) increase the frequency of Palp cycling and decrease

that of Searching. The remaining elements are scarcely affected. In the stimulus situation

SQ (pul) + @ (sph) the behaviour of males shows differences in the same way as

in the situation S? (pul) + @ (pul) regarding the elements Leg beating, Leg waving

and Palp waving. Thus, in P. pullata males, the occurrence of the complete set of

elements involved in Courtship Display (Copulation attempt, Palp and Leg waving)

is almost restricted to the situation SQ (pul) + 9 (pul).

2.2.4. Conclusions,

Males of the species studied react in different ways on the presented stimulus

situations, with respect to both the total numbers of activities and the frequencies of

particular elements.

DEN HOLLANDER, DIJKSTRA, ALLEMAN & VLIJM: Courtship behaviour in Pardosa 17

Courtship Display is elicited in P. sphagnicola by the less specific stimuli, in P. pullata

by the most specific ones. The presence of females on conspecific substrates as well as

conspecific females, independent on the nature of the substrates, stimulate P. sphagnicola

males to Courtship Display. Complete Courtship Display of P. pullata males is stimulated

by conspecific females on conspecific substrates only. In P. prativaga conspecific females

stimulate Courtship Display, independent the nature of the substrates.

On the other hand, in P. prativaga conspecific substrates as well as the presence of

females influence particular elements in the behaviour of the males. In both other

species almost only conspecific females have this effect.

A. 3. Conclusions of confrontation experiments.

The results of these experiments have shown that the behaviour of each of the species

studied is rather specific, both in quantitative and qualitative respects. Generally Court-

ship Display, the most specific part of behaviour, especially occurs in situations in which

conspecific females are present. Thus it may be concluded that the behaviour of the

species studied can be important as species barrier,

B. Breeding experiments

B. 1. Mating and egg sac construction.

The results of the breeding experiments are summarized in table 5. Any differences

between breedings with specimens from the respective collecting sites (Table 1) could

not be established.

Matings occurred in all breedings except pul g' X pra @. Although matings have

not been observed in the breedings pul X sph, (vice versa) it is evident that they had

occurred, as the females constructed egg sacs in which developing eggs could be esta-

blished.

In all breedings except pul & X pra 9 the females constructed egg sacs. The

numbers of egg sacs in the breedings sph X pul (vice versa), however, were small. Only

those egg sacs have been taken into account which were carried by the females during a

normal period of development of the eggs till the emergence of the pulli, which lasts

(under laboratory conditions) 15 - 20 days.

Many females constructed egg sacs which were abandoned after a few days. In these

Table 5. The occurrence af matings, the numbers of egg sacs constructed, the numbers of egg sacs

with developing eggs, as well as the numbers of egg sacs from which pulli emerged in six cross

breedings of the species studied

number of total num- breeding occur- number egg sacs with egg sacs from

experi- ber of rence of of egg developed which pulli

ments females matings sacs eggs emerged

4 19 pra 6 x pul 2 + 12 10 8

3 12 pul 4 x pra 2 — — — =

4 19 pra dix sph, © + 11 _ =

3 14 sph 6 x pra © (+) 9 4 3

4 24 pul 3 x sph 2 + 2 1 —

3 17 sph & x pul 9 (2) 2 2 2

18 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 1, 1973

egg sacs, the eggs always had been decayed. They were not taken into account, as,

probably, they were constructed by females which had not mated (cf. Kessler, 1969).

2. Emergence of pulli.

The eggs in the egg sacs of P. pullata females from breedings pra & X pul ©

developed normally. From eight out of twelve egg sacs pulli emerged. The same holds

for breedings sph & X pra Q, though in this case from three out of nine egg sacs

pulli emerged. On the contrary, eggs in the eggs sacs of P. sphagnicola females from

breedings pra g X sph @ did not develop at all. As matings had occurred it may

be concluded that mechanical or postmating barriers isolate P. prativaga males from

P. sphagnicola females. The precise nature of the barrier-system is yet unknown. Probably

fertilization of the eggs did not occur, as no development at all of the eggs could be

established (sperm transfer could not be directly established).

In cross-breedings of P. sphagnicola and P. pullata a rather limited number of egg

sacs were constructed. In breedings sph & X pul 2 the eggs (only two egg sacs

were constructed) developed normally and pulli emerged in a normal way. In the

reciprocal breedings the eggs developed in only one of two egg sacs produced, but no

pulli did emerge. In these breedings probably, therefore, postmating factors prevent

interbreeding, as it is likely that in the cross-breeding pul & X sph 2 fertilization

of the eggs did occur (development of eggs in one of the two egg sacs).

In conclusion, pulli could be obtained from three out of six breedings : pra & X

pul 9; sph $ X pra £; sph d X pul 9. These results allow two conclusions : first,

every species interbreeds with every other species in only one of the two reciprocal ways;

and second, P. pullata males as well as P. sphagnicola females do not interbreed with

any of the other species studied, whereas P. pullata females as well as P. sphagnicola

males interbreed with both other species.

3. Breeding of pulli.

The obtained hybrid juveniles were reared in glass jars provided with a layer of plaster

of Paris which was kept moistened. They were fed Drosophila melanogaster mutant

vestigial. The pulli grew rapidly till about four moults had occurred. Afterwards many

specimens died, especially during the moults. As the same phenomena occurred in control

breedings of both P. prativaga and P. pullata, the difficulties in breeding juveniles must

be a methodical question. As a consequence only a few juveniles reached the adult stage .

(MO prac) << pul) PP spa pra diodi

4. Conclusions.

The results show that premating barriers do not occur between P. prativaga and P.

sphagnicola, however mechanical or postmating barriers prevent the production of

juveniles from breedings pra g' X sph 9. P. sphagnicola is virtually isolated from

P. pullata by premating factors. However, this isolation is not complete. In addition,

postmating factors are effective in breedings pul & X sph 9, but they do not operate

in the reciprocal breedings (sph d X pul 9). In one of the cross-breedings of

P. prativaga and P. pullata premating factors completely prevent interbreeding (pul d'

X pra 9), whereas in the reciprocal breeding (pra 4 X pul 9) barriers are com-

pletely absent. Thus behaviour is only of minor importance in isolating the species

studied.

DEN HOLLANDER, DIJKSTRA, ALLEMAN & VLIJM: Courtship behaviour in Pardosa 19

IV. GENERAL CONCLUSIONS AND DISCUSSION

1. General conclusions.

The behaviour of males of the species studied shows qualitative as well as quantitative

differences. Males of the three species react differentially to different stimulus situations,

both in the total numbers of activities as well as in the relative frequencies of particular

activities. Complete Courtship Display in P. pullata males is only elicited in the situation

SQ (pul) + @ (pul). Conspecific females, independent of the nature of the sub-

strates, elicit Courtship Display in P. prativaga. In P. sphagnicola, besides these situations,

also conspecific substrates with females, irrespective of their nature, evoke Courtship

Display.

Under laboratory conditions every species interbreeds with every other species in only

one of the two reciprocal ways.

2. Discussion with regard to behaviour composition.

Walking and Preening occur in moderate frequencies throughout the species studied.

The mean durations of these activities, however, last longer than that of most others.

Thus both Walking and Preening contribute an important part to the total period spent.

The predominant behaviour elements differ in the three species. Palp cycling and Jerky

walking dominate in the behaviour of P. prativaga males, Searching and Courtship

Display do so in those of P. sphagnicola. P. pullata males are mainly engaged in Sear-

ching and Searching walk.

Walking and Preening.

In the behaviour patterns of the species studied the position of Preening is fixed to

a small extent only. Walking, however, contributes, together with Jerky walking and

Immobility, an important part to the patterns of both P. prativaga and P. sphagnicola.

In P. prativaga both elements are dependent in a similar way on the respective stimulus

situations. Conspecific substrates as well as the presence of females lower their fre-

quencies. In P. sphagnicola conspecific females only lower the frequency of Preening,

that of Walking being changed also by conspecific substrates. Conspecific females on

conspecific substrates lower the frequencies of both elements in the behaviour of P.

pullata males.

Palp cycling and Jerky walking.

Palp cycling and Jerky walking are closely related in the behaviour pattern of

P. prativaga; they are elicited by similar stimuli. Conspecific substrates and, to a lesser

extent, in non-conspecific females the frequencies of Palp cycling and Jerky walking

increase, in conspecific females they decrease. In both P. sphagnicola and P. pullata the

frequencies are much lower as compared with P. prativaga. In both species the elements

concerned are not connected at all with the behaviour patterns. In P. prativaga as well as

in P. sphagnicola Jerky walkings is associated with Walking and Immobility. Whereas in

P. prativaga Palp cycling closely relates to Jerky walking, it is more connected with

Searching and Leg beating in P. sphagnicola. In the pattern of P. pullata the positions

of both elements are less fixed. In both P. sphagnicola and P. pullata Palp cycling is

elicited to some extent by conspecific substrates (as in P. prativaga), Jerky walking,

however, seems not to be related to any special stimulus situation.

Searching and Searching walk.

Searching and Searching walk contribute an important part to the behaviour of

20 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 1, 1973

P. pullata males, although their frequencies being of moderate values only, the mean

durations are rather long. In the pattern Searching especially relates to Leg beating,

Searching walk is associated with Immobility. The respective stimuli exert only small

changes in both elements. Conspecific substrates lower Searching to some extent, Sear-

ching walk does not seem to be changed by any stimulus situation. The frequencies of

Searching and Searching walk are rather low in P. prativaga. In the behaviour pattern

both elements are connected with Palp cycling. Conspecific substrates, as well as con-

specific females lower the frequencies of both Searching and Searching walk. In P.

sphagnicola the frequency of Searching is also low, that of Searching walk,

however, is rather high. In pattern Searching relates to Palp cycling (as in P. prativaga)

and to Leg beating (as in P. pullata). The position of Searching walk is to some extent

comparable to that in P. pullata. Conspecific females lower the frequencies of both

elements, only Searching walk is also changed by conspecific substrates (as in P.

prativaga).

Courtship Display.

In appropriate situations Courtship Display dominates in the behaviour of P. sphagni-

cola males, The particular elements arrange a fixed pattern and behave similarly towards

the respective stimulus situations. Generally, Courtship Display is connected with the

other activities in the patterns through Immobility and is elicited by conspecific females

only. However, in P. sphagnicola non-conspecific females occuring on conspecific sub-

strates also evoke Courtship Display. Comparable activities contribute to Courtship Dis-

play in P. prativaga and in P. sphagnicola. In P. prativaga Courtship Display never

dominates the behaviour of the males. Courtship elements of both P. prativaga and

P. sphagnicola hardly occur in P. pullata. On the other hand, this species shows Courtship

Display, the elements of which hardly occur in both former species. Courtship Display

takes a very small part in the behaviour of P. pullata males only.

One of the elements of Courtship Display in P. pullata, Leg waving, also occurs in

P. sphagnicola. However, in this species conspecific females lower its frequency and the

position in the patterns is different. Leg waving as well as Leg beating do not occur

in P. prativaga. The frequency of Leg beating is of the same level in both P. sphagnicola

and P. pullata. In the pattern of both species it is close to Searching. Similar stimuli

lower its frequency in both species, viz., conspecific females. Conspecific substrates also

lower Leg beating to some extent in P. sphagnicola only.

3. Discussion with regard to interbreeding.

In the context of interbreeding, Courtship Display and its eliciting factors are

important. Courtship Display dominates in P. sphagnicola and is elicited in rather un-

specific situations too. In P. prativaga and especially in P. pullata Courtship Display never

dominates the behaviour of the males and only occurs in specific situations. Thus

it may be concluded that the behaviour of P. sphagnicola males presents the weakest

factor in preventing interbreeding as compared to that of both P. prativaga and P.

pullata.

Indeed, in breeding experiments P. sphagnicola males mated with females of both

other species, especially P. prativaga females. However, matings occur in all breedings

except pul & X pra ©. In all cases matings result in egg sac construction. Hybrid

juveniles have been obtained in only three out of six breedings, viz., pra d X pul 9,

sph ¢ X pra 2 and sph & X pul ©. Behavioral factors isolate P. pullata males

DEN HOLLANDER, DIJKSTRA, ALLEMAN & VLIJM: Courtship behaviour in Pardosa 21

from P. prativaga females, whereas postmating or mechanical factors isolate P. sphagni-

cola females from both P. prativaga and P. pullata males. In the barrier between P.

pullata and P. sphagnicola, however, behavioral factors are involved to some extent too.

4. Discussion with regard to isolating mechanisms.

Preceding studies have shown that seasonal, as well as habitat factors operate in

isolating the species studied. P. sphagnicola exclusively occurs in peat-moor swamps

(Dahl, 1908; Holm & Kronestedt, 1970) whereas both P. pullata and P. prativaga

occur in less specific habitats (Dahl, 1908; Wiebes, 1959), although differences occur

(Den Hollander & Lof, 1972). Both P. prativaga and P. pullata occur in populations of

P. sphagnicola, though in very small numbers, especially P. prativaga. True mixed

populations of P. prativaga and P. pullata, on the other hand, do occur. Thus P. sphag-

nicola is isolated from P. prativaga and, to a lesser extent, from P. pullata, by habitat.

P. prativaga males are isolated completely from P. pullata females by seasonal factors,

as P. pullata females have already mated and are constructing their egg sacs when

P. prativaga is going through its last moult and becoming adult. Adult males of both

P. sphagnicola and P. pullata occur in the same period as unmated females of the other

species (Den Hollander, 1971).

Thus habitat isolation prevents interbreeding between P. sphagnicola and both P.

prativaga and P. pullata. Furthermore, P. sphagnicola females are isolated from males

of both other species by mechanical or postmating barriers. The habitat barrier between

P. sphagnicola and P. pullata is not complete. However it is compensated by the

existence of, though not complete, behavioral barriers. Behavioral barriers only prevent

cross breedings of P. prativaga females and P. pullata males, the reciprocal breedings

being prevented by seasonal barriers.

These results show that specificity of Courtship behaviour of wolf spider males does

not imply that it should play an important role in isolating species. It is more likely

that only then when other barriers are broken down, e.g. when two species become

syntopical, the existing differences in behaviour are embraced to evolve reproductive

isolation.

V. SUMMARY

1. Species of the Pardosa pullata group (P. pullata, P. prativaga and P. sphagnicola)

were studied as to specific differences in behaviour of the males towards both con-

specific and non-conspecific substrates and females.

2. Qualitative, as well as quantitative differences occur between the behaviour of

males of the respective species,

3. Males of the species studied react differentially to the presented stimulus

situations.

4. In the laboratory every species interbreeds with every other species in only one

of the two reciprocal ways. Under natural conditions these cross-breedings mostly are

prevented by seasonal and habitat factors.

5. It is concluded that behavioral factors are of minor importance in isolating the

species of the P. pullata group. However, differences in behaviour have been evolved

to species barriers in sympatric situations.

22 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 1, 1973

VI. ACKNOWLEDGEMENTS

The authors are indebted to Mr. G. W. H. van den Berg for preparing the illustrations,

and to Miss E. C. Gräper for typing the manuscript.

Dijkstra acknowledges the financial support of the Organization for Pure Scientific

Research (Z.W.O.).

VII. REFERENCES

Bristow, W. S. & G. H. Locket, 1926. — The courtship of British spiders and its probable

significance. — Proc. Zool. Soc. 22: 317—347.

Dahl, F., 1908. — Die Lycosiden oder Wolfspinnen Deutschlands und ihre Stellung im Haushalte

der Natur. — Nova Acta Acad. Caes. Leop.—Carol. 88: 177—558.

Dijkstra, H., 1969. — Comparative research of the courtship behaviour in the genus Pardosa

(Arachn., Aranae) III. Agonistic behaviour in Pardosa amentata. — Bull. Mus. His. Nat.

41: 91-97. :

Dijkstra, H., S. W. F., van der Ploeg & M. J. Koomans. — Leg-wave behaviour in the genus

Pardosa (Araneae, Lycosidae). — In preparation.

Hallander, H., 1967. — Courtship display and habitat selection in the wolf spider Pardosa chelata

(O. F. Miiller). — Oikos 18: 145—150.

Hollander, J. den, 1970. — Morphological variation in Pardosa prativaga (L. Koch, 1870), P.

prativaga var. fulvipes (Collet. 1875), and P. pullata (Clerk, 1757) (Araneae, Lycosidae).

— Tijdschr. Entomol. 113: 273—288.

, 1971. Life-histories of species of the Pardosa pullata group, a study of ten populations

in the Netherlands (Araneae, Lycosidae). — Tijdschr. Entomol. 114: 255—281.

Hollander, J. den & H. Lof. 1972. — Differential use of the habitat by P. prativaga (L. Koch)

and P. pullata (Clerck) in a mixed population (Araneae, Lycosidae). — Tijdschr. Entomol.

115: 205-215.

Hollander, J. den, L. Vlijm, H. Dijkstra & S. C. Verhoef, 1972. — Further notes on the occurrence

of the genus Pardosa in Southern France (Araneae, Lycosidae). — Beaufortia 20 (264) :

77— 84.

Holm, A. & T. Kronestedt, 1970. — A taxonomic study of the wolfspiders of the Pardosa pullata

group (Araneae, Lycosidae). — Acta ent. bohemoslov. 67: 408—428.

Kessler, A., 1969. — Egg production in Pardosa. Influence of mating on the egg-ripening period

in Pardosa lugubris (Walck.) (Araneae, Lycosidae). — Bull. Mus. His. Nat. 41: 98—101.

Locket, G. H. & A. F. Millidge, 1951. — British spiders, vol. 1. — London.

Mayr, E., 1940. — Speciation phenomena in Birds. — Amer. Natural. 74: 249—278.

, 1969. — Animal species and evolution. — Harvard Univ. Press. Cambridge.

Richter, C. J. J., 1970. — Morphology and function of the spinning-apparatus of the wolfspider

Pardosa amentata (Cl.) (Araneae, Lycosidae). — Z. Morph. Tiere 68: 37—68.

Richter, C. J. J., J. den Hollander & L. Vlijm, 1971. — Differences in breeding and mobility

between Pardosa pullata (Clerck) and Pardosa prativaga (L. Koch) (Lycosidae, Araneae)

in relation to habitat. — Oecologia 6: 318—327.

Vlijm, L. & W. J. Borsje. 1969. — Comparative research of the courtship behaviour in the genus

Pardosa (Arachn., Araneae) II. Some remarks about the courtship behaviour in Pardosa

pullata (Clerck). — Bull. Mus. His. Nat. 41: 112—116.

Vlijm, L. & H. Dijkstra, 1966. — Comparative research of the courtship behaviour in the genus

Pardosa (Arachn., Araneae) I. Some remarks about the courtship of P. amentata, P. hor-

tensis, P. nigriceps and P. lugubris. — Senck. biol. 47: 51—55.

Vlijm, L., J. den Hollander & S. E. Wendelaar Bonga, 1970. — Locomotory activity and sexual

display in Pardosa amentata (Cl.) (Lycosidae, Araneae). — Neth. J. Zool. 20: 475—484.

Wiebes. J. T., 1959. — The Lycosidae and Pisauridae (Araneae) of the Netherlands. — Zool.

Verh. 42: 1—78.

No. 2. P. J. Brakman, 1966. — Catalogus van Coleoptera uit Nederland en het omliggende

bied (List of the Coleoptera of the Netherlands and adjacent region), 219 pp., map. D.FI. 45.—.

No. 3. G. A. Graaf Bentinck en A. Diakonoff, 1968 — De Nederlandse Bladrollers (Tortricidae),

„(The Netherlands Leaf-Rollers (Tortricidae)). 350 pp. en 98 pl. D.FI. 70.—.

| No. 4. F. Willemse, 1968. — Preliminary revision of the genera Stenocatantops Dirsh & Uvarov

End Xenocatantops Dirsh & Uvarov (Orthoptera, Acridiidae Catantopinae), 77 pp., 1 map, 6 pl.

D.FI. 25.—.

| No. 5. C. A. W. Jeekel, 1970. — Nomenclator generum et familiarum Diplopodorum, 412 pp.

“DFI. 100.—.

| No. 6. J. G. Betrem, 1971. — The African Campsomerinae (Hymenoptera, Scoliidae), 326 pp.,

47 Do 6 pls. D.Fl. 120.—.

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A COMPARATIVE STUDY OF THE PRODUCTION OF EGGS IN

EIGHT PARDOSA SPECIES IN THE FIELD

(ARANEAE, LYCOSIDAE)

A. KESSLER

Department of Biology, Free University, Amsterdam

ABSTRACT

The egg production of eight common Pardosa species in the Netherlands, estimated from field

samples, is described. Samples were taken on the same spot during five years for six species

(1966—1970). In 1968 some species were sampled extensively in several parts of the Netherlands.

Intra- and interspecific differences in egg production were found to be related to the size of the

mother spiders. Factors influencing intraspecific differences in size of the spiders are discussed.

INTRODUCTION

The relation between food consumption and egg production in spiders has been

dealt with by Turnbull (1962) in Linyphia triangularis. Data on Lycosid spiders in

general are scarcely known (cf. Edgar, 1968, 1971). Kessler (1971) studied this relation-

ship in four species of Pardosa under experimental conditions. These results, however,

should be compared with data on natural populations. This paper deals with data on egg

production of eight species of Pardosa in the field, estimated from samples taken in

natural populations. The results are discussed in relation to data from the literature as

well as in relation to experimental data (Kessler, 1971; Turnbull, 1962, 1965).

MATERIAL AND METHODS

AII samples were made by hand-collecting female spiders carrying egg sacs. Care

was taken to collect specimens in the period when all females were carrying egg sacs,

viz., in the middle of the reproductive period, so that a sample is representative for all

females in the population.

Eight species were sampled in 1968 in different localities throughout the country,

six species were sampled from 1966 to 1970 yearly in the same locality.

A description of the habitat of the species concerned in the Netherlands is given

by Richter (1970).

It is only possible to collect spiders in sufficient quantities when the weather is

bright. This seriously narrows down the time available for sampling. Moreover, the

period in which the females are carrying the egg sacs is about the same for all species

(the middle of May until the end of June). For these reasons some samples in the

series are missing or incomplete.

In each sample a number of spiders were collected which were missing one or more

legs. The egg sacs of these specimens are not considered in this paper. The same holds

24 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 2, 1973

for egg sacs containing egg sac parasites (Hymenoptera). The latter are dealt with

elsewhere (Kessler & Fokkinga, 1973).

Every specimen collected was kept separately, so that relations between mother

spider and offspring could be studied.

A positive correlation between size of the mother spider and number of offspring

has been demonstrated in the genus Pardosa by Petersen (1950). In order to investigate

this phenomenon interspecifically one should either calculate regression lines for each

species or express the number of eggs as a ratio of spider size. The latter method is

used in this paper because the calculations are simple and the method gives a more

direct insight, when comparisons are made interspecifically. The dryweight of carapaces,

including the legs, is used as an estimate for spider size. Carapaces were dried in an

oven at 60° C.

For statistical method Duncan’s new multiple range test with Kramers modification

for inequal sample size was used (a = 0.05).

RESULTS

I. COMPARISON OF THE SPECIES

In 1968, the eight common species of Pardosa, viz., Pardosa amentata (Clerck),

P. lugubris (Walck.), P. pullata (Clerck), P. prativaga (L. Koch), P. nigriceps (Thorell),

P. purbeckensis F.O.P.-Cambridge, P. monticola (Clerck) and P. palustris (L.), were

sampled in order to compare the species as to the amount of egg production.

The data on numbers of eggs per egg sac (1), the dryweight of the carapaces (2)

and the numbers of eggs per mg carapace dryweight (3) are shown together in table 1

and are discussed separately in the following chapters.

a. Number of eggs

The mean numbers of eggs in the egg sacs range from 86.2 in P. amentata to 26.6

in P. monticola. In Graph 1 the frequencies are shown; Graph 2 gives the range of the

values and the means for all species together. Three separate groups can be distinguished

(though sometimes a considerable overlap has been found).

P. amentata SE 85 ELIS

P. palustris, P. prativaga and P. purbeckensis + 50 eggs

P. lugubris, P. pullata, P. nigriceps and P. monticola + 30 eggs

In some egg sacs undeveloped eggs were found. They are easily recognized, even at

very early stages in the development of the egg batch, by a brownish colour (normal

eggs are white). Table 1 illustrates that the number of undeveloped eggs is never

high. The great varibility is due to the fact, that in most egg sacs only 1 or 2 undeveloped

eggs are found, whereas in a few others more than half of the eggs are undeveloped.

b. Size of spiders (carapace dryweight)

The differences in carapace dryweight between the species are rather small, with the

exception of P. amentata (Table 1). None of the species does show any overlap in values

with P. amentata (Graph 1). In this group of species P. monticola and P. pullata can

A. KESSLER: Production of eggs in Pardosa species

40-

P. lugubris

P amentata

30-

20-

10-

P. pullata

P.nigriceps

P. palustris

P. prativaga

P.monticola

P.purbeckensis

[un

2481 - 500%

2441 - 4602

2401 - 4203

= 361 - 380 >

2.321 - 340%

2281 - 3008

= 241 - 2605

= 201 - 220

= 161 - 180

RARE:

les)

2761 - 7808

2721-7402

2681-700 ®

2641 -660 È

2601 - 620%

= 561 -580 5

2521 -540 5

2481 -500 °

2441 -460

2401 -420

= 361 -380

= 321 -340

= 281 - 300

2241 -260

= 201-220

106 -110 ©

96 -100 D

RENE

(©)

Graph 1. Frequency diagrams of the number of eggs and the dryweight of the carapaces (in 0.01 mg)

of eight Pardosa species

TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 2, 1973

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A. KESSLER: Production of eggs in Pardosa species 27

——_————————————_—__—+_+—_-_—_—*w«.;+-—.,;--gryy-- am

[ume pal

mm a, prat

e purb

e lug

| pull

I DI nigr

SS < mont

RE am

ef prat

SS SS purb

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——f nme pal

— +———— nigr

ee à— pull

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eS ee pen

1.00 2.00 3.00 400 5.00 6.00 7.00 8.00 9.00 mg carap.

dry weight

e e pal

ey prat

— purb

TT am

lite fo er pull

ee mont

fe lug

= — nigr

4 8 12 16 20 24 28 number of eggs / mg carap. dry weight

Graph. 2. Range of values and means of number of eggs per egg sac, carapace dryweight and number

of eggs per mg carapace dryweight of eight Pardosa species. (For further explanation see table 1.)

be distinguished by their carapace weight (2.3 and 2.4 versus + 3 mg). Furthermore

it should be noted that in most species different size groups are found (Graph 1).

Probably these differences are caused by the presence of spiders born from the first

egg sacs as well as from the second egg sacs of last year.

c. Number of eggs per mg carapace dryweight

The data in table 1, Graph 2, and Graph 3, show that any differences in the values

of number of eggs per mg carapace dryweight are not conspicuous. This leads to the

conclusion that in general the size of the spider species determines the number of

offspring.

An exception is found in P. palustris. In this species, under field conditions, con-

siderably more eggs are produced per unit of size than in the other species. This is in

28 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 2, 1973

%_ P amentata a P lugubris

20- =

10- =

0- =

* P palustris > P pullata

20- =

10- -

O5 =

30- P prativaga = P nigriceps

20- =

10- -

0- =

P purbeckensis P monticola

20- =

10- -

0- fa

LI ries RA PS. age Tee eh [OT LA TAN NE AS ST] Kl SE Wo et eet UO LI LJ De AD

10 12 14 16 18 20 22 eggs Mg: 6 8 10 12 14 16 18 eggs

Graph 3. Frequency diagrams of the number of eggs per milligram carapace dryweight of eight

Pardosa species

agreement with the data of Kessler (1971), which showed that under experimental

conditions P. palustris produces more eggs per unit of size than the other investigated

species, because the eggs are lighter.

II. COMPARISON OF SAMPLES FROM DIFFERENT LOCALITIES IN THE SAME YEAR

Samples from different localities in 1968 (Fig. 1) were avaiable from P. amentata,

P. pullata, P. purbeckensis, P. nigriceps, P. monticola and P. prativaga. The results

are shown in table 2.

A. KESSLER: Production of eggs in Pardosa species 29

ESSE

es,

Fig. 1. The geographic position of the different sampling localities in the Netherlands in 1968

(1 = Schiermonnikoog, 2 = Weerribben (P. prativaga), 3 = IJsselmeerpolder, 4 = Surroundings

of Amsterdam (P. amentata), 5 = Hollandsche Rading, 6 = Oostvoorne)

a. Number of eggs.

In P. amentata the mean number of egg in locality 4 is relatively low (62.9).

The difference between the other three localities (72.9—86.2) are not conspicuous. The

localities 1, 2 and 3 are situated in the normal habitat of P. amentata in the Netherlands,

viz. along ditches in meadows. Locality 4 is a piece of wasteland with heaps of black

earth along a ditch. The density of P. amentata is relatively high there. In this locality

the same number of specimens as at the other localities was collected in a much shorter

period.

In P. pullata only locality 5 shows a very low number of eggs per egg sac (24.5).

These specimens were collected on small, newly formed dunes, near the beach of the

Frisian island Schiermonnikoog. The other localities (1 to 4) are situated on Schiermon-

nikoog and in Hollandsche Rading.

In P. purbeckensis two groups can be distinguished, on account of the number of

eggs: spiders from localities 1 and 2 (65.0 and 58.1 eggs) and from 3 and 4 (47.1

and 42.8 eggs). Localities 3 and 4 are situated in the normal habitat of the species,

viz., salt marshes between tidal creeks on Schiermonnikoog. Locality 1 is situated in a

recently made polder in the IJsselmeer; locality 2 on the island Oostvoorne, where

a tidal salt marsh is enclosed by a dike.

In P. nigriceps the only difference between the localities is their geographical position:

9YT

TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 2, 1973

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A. KESSLER: Production of eggs in Pardosa species 31

Oostvoorne (1) versus Schiermonnikoog (2). The same holds for P. monticola: Holland-

sche Rading (1) versus Schiermonnikoog (2).

In P. prativaga locality 1 is the normal habitat of the species in the eastern part of

the Netherlands, while locality 2 is the same as locality 2 of P. purbeckensis (Oost-

voorne).

b. Size of spiders (carapace dryweight).

As the localities in table 2 are arranged according to decreasing mean number of

eggs, it is easy to see in column 2 of table 2 that the dryweight of the carapace

decreases in relation to the number of eggs. The same applies here as to the mean number

of eggs in the different species (c.f. paragraph a).

c. Number of eggs per mg carapace dryweight.

In general the number of eggs per mg carapace dryweight shows the same trend as

the dryweight of the carapace and the number of eggs, except in P. pullata, where

there are no significant differences in the values (table 2).

A decreasing number of eggs corresponds with a decrease in size and a decrease in

number of eggs per mg carapace dryweight. It seems that there is a correlation between

size and number of eggs per unit of size. This correlation, however, could not be

demonstrated in separate samples. This implicates that the values for carapace dryweight

and number of eggs per mg carapace dryweight vary independently of each other.

This does not mean that the reason why spiders in some localities stay smaller and

produce less eggs per unit of size cannot be found in the correlation between size and

number of eggs per unit of size.

III. COMPARISON OF SAMPLES FROM THE SAME LOCALITIES IN SUBSEQUENT YEARS

From some localities — the specific habitats of the species concerned — each year,

from 1966 to 1970, a sample of females with egg sacs was taken. This was done for

P. amentata, P. pullata, P. nigriceps, P. purbeckensis, P. monticola, P. lugubris and

P. palustris (the last species only in 1966 and 1968). The results are shown in table 3.

a. Number of eggs.

It is clear from table 3, that in general the mean number of eggs in a population

is kept at a fairly constant level. In each species there are no significant differences

in numbers of eggs in different years. Most striking is the situation in P. pullata and

P. lugubris where in 4 out of 5 and 3 out of 4 years, respectively, almost the same

mean numbers of eggs were found. P. amentata is more or less an exception since the

numbers of eggs agree for two years at the most. In the case of P. palustris no con-

clusions can be drawn because of lack of data.

However, it is clear that in some years either comparatively high or low values

occur. From column 6 in table 3, it is concluded that there are no specific “good” or

“bad” years for the whole group of species.

b. Carapace dryweight.

A constancy in carapace dryweight during the years has been found. This seems to

agree with the data on the mean number of eggs, although they are not directly

TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 2, 1973

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34 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 2, 1973

comparable. “Good” or “bad” years for size mostly do not coincide with “good” or

“bad” years for egg production.

c. Number of eggs per mg carapace dryweight

This value is also rather constant in all species. Striking are the extremely high values

of P. amentata in 1966 and P. pullata in 1966. In both cases this high value compensates

the low value in carapace dryweight, resulting in a normal number, in P. pullafa even

the highest number, of eggs. This is not the case in P. purbeckensis in 1970, where

the effect of a low value in carapace dryweight on egg production is strengthened by

a low value in number of eggs per mg carapace dryweight.

In general there is no correlation between carapace size and number of eggs per mg

carapace dryweight, as can be easily seen in comparing columns 7 and 8 of table 3.

IV. SECOND EGG SACS

In a few species samples of spiders with second egg sacs could be taken. The data

are compared with samples of the first egg sac from the same locality (table 4). The

number of eggs in the second egg sac is about 50 to 60 0/9 of the number in the first

egg sac. The size of the spiders (except P. nigriceps) is the same in first and second

egg sac samples. Thus it may be concluded that the production per mg carapace

dryweight is much lower for the second egg sac.

V. EVALUATION OF THE RESULTS

A summary of the data on egg production of the Pardosa species concerned in this

paper is given in Graph 4 where the ranges of mean values from all the samples are

shown for the eight species of Pardosa.

The differences in egg production between the species are mainly caused by differences

in size. Larger species produce more eggs than smaller species.

This does not seem to hold when a species produces eggs which weigh less. In this

case (c.f. P. palustris) more eggs are produced than should be expected on account

of the size.

Intraspecific differences.

Differences in subsequent years in the same locality.

Any differences occurring in egg production can be caused by climate, habitat or food.

Climate. — In general the period of growing up for all species as well as their

breeding periods, coincide. Therefore, the influence of good or bad weather conditions

should be manifest in all species in the same way. As this is not the case, it can be con-

cluded that no clear influence of climatic conditions can be observed.

Habitat, — In the successive years the habitats studied remained constant. This is

also clear from the fact that no trend in egg production, indicating a gradual change

in habitat in the course of the years, could be demonstrated. Differences in egg produc-

tion, therefore, cannot be caused by differences in habitat conditions.

A. KESSLER: Production of eggs in Pardosa species

Re << am

———= 4 pal

oad prat

pee purb

— lug

al pull

nea nigr

EE mont

=. pal

— prat

i purb

lug

pull

pen) nigr

(sem) mont

GER

100 200 3.00 4.00 5.00 6.00 mg carap.

dry weight

= am

—-. pal

— prat

iero: Sheetal purb

ml lug

an ee pull

uni nigr

pl mont

lr Erre FAR

4 8 12 16 20 number of eggs/ mg carap.

dry weight

Graph 4. Ranges of mean values of number of eggs per egg sac, carapace dryweight and number

of eggs per mg carapace dryweight, based on all samples that are discussed in this paper

36 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 2, 1973

Food. — Two components can be distinguished in relation to egg production:

1) Availability of the food: the total quantity of food that is available.

2) Accessibility of the food: that part of the total quantity of food that can be

obtained by spiders.

Availability of the food.

One should distinguish between two periods in the life-time of a spider: the period

of growing up and the egg-ripening period during the breeding season. Differences may

occur in quantity of food available during the time of growing up as compared to the

quantity of food available during the egg-ripening period. Large quantities of food

during the time of growing up will result in large spiders. However, when during the

egg-ripening period the quantity of available food is small, relatively few eggs per unit

of size will be produced (e.g. P. purbeckensis in 1969 in table 3).

It is also possible, that small specimens produce much more per unit of size than the

larger specimens, indicating that the food situation is better during the breeding season

than during the time of growing up (e.g. P. amentata in 1966 in table 3).

Accessibility of the food.

Differences in density of the spiders can be of importance here, as higher densities

of spiders will mean a smaller amount of food for every individual, Though no pertinent

observations have been made on this point, there are no reasons to assume that there

are considerable differences in density from year to year.

If there is enough food available the possibility remains that the animals periodically

lack opportunities to catch food. Under high temperatures (+ 40° C) the spiders

become inactive and this diminishes the chance of meeting prey. At the same time

metabolic processes continue and, at a certain moment, the animals are due to produce

an egg sac (Kessler, 1969). At low temperatures (+ 10° C) the spiders are inactive

too, and although metabolic processes are retarded then, they do not stop entirely. This

causes the same effect, though on a lesser scale, as in the forementioned case.

The same reasoning probably holds for the period between two moults. The length

of time between two moults is, as is the case with the egg-ripening period, mainly

determined by temperature. Food plays a minor role in this process (Turnbull, 1965).

In conclusion we may state, that in the same habitat in different years, differences

in size of the spiders and differences in egg production per unit of size are caused by

differences in food intake of the spiders. In general this does not lead to considerable

differences in the mean number of eggs per egg sac.

Differences between localities in 1968.

As all three factors mentioned, viz., climate, habitat and food, might be of influence,

they are evaluated here.

Climate. — There are certain differences in macroclimate between the different

localities (e.g. Schiermonnikoog in the north of the Netherlands, Oostvoorne in the

south). It is not clear if these differences are also reflected in differences in microclimate

between the localities.

Habitat. — The clear difference in habitat in some localities, (e.g. P. purbeckensis

A. KESSLER: Production of eggs in Pardosa species 37

in salt marshes and in new polders; P. amentata in waste land and along ditches in

meadows; table 2 also shows clear differences in egg production.

Food. — It is assumed that any differences in climate and difference in habitat

structure in most cases only can have influence on egg production via food.

It is evident that not in all places the egg potential of the species is realized in an

optimal way. This provides an opportunity to evaluate habitats as suitable or unsuitable

for the development and the egg production of Pardosa species. However, it is not clear

whether a large size and a high egg production can be considered an advantage or a disad-

vantage for the population of a species (e.g. P. amentata in a piece of waste land, table 2;

the egg production and the size show low values, whereas the density of the population

is rather high).

Second egg sac.

Not all species construct a second egg sac, at least not in large quantities. The

meaning of the second egg sac for the survival of the species is not clear.

The lower number of eggs in second egg sacs compared with first is probably caused by

a lower potential number of eggs for the second egg sac. This can be deduced from

laboratory experiments (unpublished data), where the spiders consumed less food during

the second egg-ripening period, as compared with the first egg-ripening period, under the

same experimental conditions.

General conclusions.

There are specific differences in size. The size determines the egg potential of the

spider. The size is determined by the quantity of food consumed by the spider. This is

influenced by the geographical position of the habitat (differences in climate) and

differences in habitat structure.

For the effectuation of the egg potential (egg production per unit of size) the same

can be said. However, differences in weight of the eggs can decrease or increase the egg

potential of a species as compared to other species.

In determining size and effectuation of egg potential, food is the most important

factor.

VI. DISCUSSION

Dahl (1908) gives some data on number of eggs per egg sac in Pardosa species,

with references to several authors. Wiebes (1959) describes the number of eggs in

Pardosa species, and Den Hollander (1971) and Richter et al. (1971) do the same

especially with regard to P. pullata and P. prativaga in the Netherlands. Graefe (1964)

gives some information on a few Pardosa species from Germany and Petersen (1950),

on some species from Sweden. Edgar (1971) produces data on numbers of eggs in

P. lugubris in Scotland. The data are summarized in table 5. There is a wide variety in

number of eggs produced in a species. Partly this may be caused by the fact that some

authors did not study enough specimens in definite populations to gain reliable results.

Furthermore it should be noted that the data are not discussed with reference to

the size of the spider which carried egg sacs. From the present study it is clear that any

38 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 2, 1973

Table 5. Number of eggs per egg sac, data from literature (data from the present paper are derived

from the mean values found in different populations of the species)

Spider species Number of eggs Author Country

per egg sac

P. amentata 60—70 Dahl (Sundevall) Sweden

= 50 Dahl (Blackwall) England

75—100 Dahl (Becker) Belgium

60 Dahl (Henking) Germany

50—70 Wiebes Netherlands

34 Graefe Germany

60—85 Kessler (present paper) Netherlands

P. pullata 25 Dahl (Blackwall) England

36 Dahl (de Lessert) Switzerland

25—30 Wiebes Netherlands

26—44 Den Hollander Netherlands

30—37 Richter Netherlands

27 Petersen Sweden

25—35 Kessler (p.p.) Netherlands

P. prativaga 33 Graefe Germany

42—52 Den Hollander Netherlands

47—52 Richter Netherlands

36 Petersen Sweden

50—60 Kessler (p.p.) Netherlands

P. lugubris 50 Dahl (Blackwall) England

40—70 Dahl (Becker) Belgium

25-30 Wiebes Netherlands

24 Graefe Germany

37 Edgar Scotland

35—40 Kessler (p.p.) Netherlands

P. nigriceps Æ 30 Wiebes Netherlands

30—40 Kessler (p.p.) Netherlands

P. monticola 50 Dahl (Sundevall) Sweden

50—60 Dahl (Blackwall) England

30—40 Dahl (Becker) Belgium

È 40 Wiebes Netherlands

39 Graefe Germany

29 55 Kessler (p.p.) Netherlands

P. palustris + 40 Wiebes Netherlands

42 Petersen Sweden

45—55 Kessler (p.p.) Netherlands

P. purbeckensis 30—65 Kessler (p.p.) Netherlands

study dealing with egg production in Pardosa species in relation to their geographic

distribution should account for the size of the spiders at the same time.

In a former paper (Kessler, 1971) I reported on the relation between food con-

sumption and egg production of some Pardosa species under experimental conditions

A. KESSLER: Production of eggs in Pardosa species 39

Table 6. Comparison between experimental data on egg production (Kessler, 1971) and range of

mean numbers from field samples (present paper)

Experiments Field samples

Spider species Number Carapace N Number Carapace

of dryweight of dryweight

eggs eggs

P. amentata 85.4 7.65 10 62.9—86.2 5.00-—5.90

P. lugubris 46.8 4.59 4 33.9—40.5 3.11—3.63

P. palustris 63.0 4.38 4 42.5—54.2 2.83—3.03

P. monticola 51.0 4.64 4 26.6—36.7 2.19—2.47

in the laboratory. The spiders were kept separately in glass jars and were given an

abundant food supply of Drosophila melanogaster.

The results of these experiments show much higher values in egg production than

found in the field samples. Table 6 summarizes these differences. The most striking

is the large size of the spiders in the experiments. The higher amount of eggs

produced must be considered a natural consequence of this larger size. The question

is why these animals were so much larger than the animals in the field samples. They

have been caught in the same localities in which the field samples were collected. All

experimental animals, however, were kept for some weeks in the laboratory before

moulting to adults. During that time they were also given an abundant food supply.

This can account for their larger size, assuming that in nature, during the period before

moulting to adults (very early spring), they are not able to catch abundant food. There

is evidence (Turnbull, 1962, 1965), that spiders when given small amounts of food

go on growing and moulting, although the period between two moults is much longer

and the spiders stay smaller. These observations indicate that, under field conditions,

indeed food may be a limiting factor in egg production, directly or via the size of the

spiders. In the same paper (Kessler, 1971) the reaction was described of Pardosa species

on increasing food shortages after moulting to adult.

It was clear that all four species (viz., P. amentata, P. lugubris, P. palustris and

P. monticola) adapt their egg production to the food supply. However, P. amentata and

P. monticola showed a quicker reaction than P. palustris and P. lugubris. The egg

ripening period, viz., the length of the period between moulting and egg laying, proved

to be mainly dependent on “climate”, not on food.

The species concerned also showed the tendency to produce lighter eggs under con-

ditions of food shortage. This phenomenon slightly compensated the lower amount of

egg biomass produced.

Combining the results of Turnbull (1962, 1965), my experimental results (Kessler,

1971) and the field data from the present paper, it can be stated that:

1. The size of the adult spider is dependent on the quantity of food available during

the developmental period. Conditions of climate and habitat probably influence the

availability of food during this period.

2. The quantity of food available during the egg-ripening period then determines

the effectivity of the potential number of eggs, that can be deposited according to size.

By a decrease in weight of the individual eggs the potential number of eggs can be

increased, The amount of egg production in combination with the size of the adult

40 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 2, 1973

spiders can give an indication of the suitability of the particular locality where the

species is sampled.

Den Hollander (1971) states that, although there is a rather sizable difference in

number of eggs in the first egg sac between P. pullata and P. prativaga, the difference

is annihilated by the fact that the species with fewer eggs in the first egg sac (P. pullata)

produces a second egg sac more often than P. prativaga. No direct data on the other

species in this paper are available, but indirect data (e.g. the much greater effort to

sample second egg sacs of P. amentata compared with P. nigriceps) indicate that this

phenomenon may be of common interest in spiders of the genus Pardosa.

Before speculating on the meaning of the higher number of eggs in the first egg sac

in bigger species, more data on the second egg sac of Pardosa species should be available.

SUMMARY

The egg production of eight Pardosa species (Araneae, Lycosidae) in the Netherlands

is described on the basis of field samples. The eggs are deposited in an egg sac, which

is carried around by the female spider on the spinnerets,

The first egg sac seems to be the most important one for reproduction, although some

species sometimes produce a second egg sac, containing much less eggs than the first.

The mean number of eggs in the first egg sac ranges from + 86 in Pardosa amentata

to + 25 in Pardosa monticola. The number of eggs produced is dependent on the size

of the spiders.

Intraspecific differences occur as to the number of eggs and size of the spiders between

populations from different localities in the same year. In the same locality no obvious

differences in egg production could be found in subsequent years in different species.

It is concluded that differences in size and differences in egg production between

populations are mainly caused by differences in food intake of the spiders.

ACKNOWLEDGEMENTS

I should like to thank Prof. Dr. L. Vlijm for his valuable criticism and help during

the investigations and with preparing the manuscript. I am deeply indebted to Mrs. M. N.

Giardina-Wind and Mr. S. C. Verhoef for their help in collecting numerous data on

egg sacs and spiders. I am indebted to Mr. G. W. H. van den Berg for drawing the

figures and to many other people for their assistance in collecting spiders,

REFERENCES

Dahl, F., 1908. — Die Lycosiden oder Wolfspinnen Deutschlands und ihre Stellung im Haushalte

der Natur. — Nova Acta Acad. Caes. Leop. Carol. 88: 177—558.

Edgar, W. D., 1968. — Aspects of the ecology of the wolf spider Lycosa lugubris (Walckenaer).

— Thesis, University of Glasgow.

, 1971. — Seasonal weight changes, age structure, natality and mortality in the wolfspider

Pardosa lugubris Walck. in Central Scotland. — Oikos 22: 84—92.

Graefe, G., 1964. — Die Brutfürsorge bei Pardosa lugubris (Walckenaer) (Araneae, Lycosidac).

— Thesis Miinchen. ‘

Hollander, J. den, 1971. — Life-histories of the species of the Pardosa pullata group, a study of

ten populations in the Netherlands (Araneae, Lycosidae). — Tijdschr. Entom. 114 (8):

255—281.

A. KESSLER: Production of eggs in Pardosa species 41

Kessler, A., 1969. — Egg production in Pardosa. Influence of mating on the egg-ripening period

in Pardosa lugubris (Walckenaer) (Araneae, Lycosidae). — Bull. Mus. Nat. Hist. Nat.

Paris 41: 98—101.

—, 1971. — Relation between Egg Production and Food consumption in Species of the genus

Pardosa (Lycosidae, Araneae) under Experimental Conditions of Food-Abundance and

Food-Shortage. — Oecologia 8: 93—109.

Kessler, A., & Fokkinga, A., 1973. — Hymenopterous parasites in egg sacs of spiders of the Genus

Pardosa (Araneae, Lycosidae). — In press.

Petersen, B., 1950. — The relation between size of mother and number of eggs and young in some

spiders and its significance for the evolution of size. — Experimentia (Basel) 6: 96—98.

Richter, C. J. J., 1970. — Relation between Habitat Structure and Development of the Glandulae

ampullaceae in Eight Wolfspider species (Pardosa, Araneae, Lycosidae). — Oecologia 5:

185—199.

Richter, C. J. J., J. den Hollander & L. Vlijm, 1971. — Differences in Breeding and Motility

between Pardosa pullata (Clerck), and Pardosa prativaga (L. Koch) (Lycosidae, Araneae)

in Relation to Habitat. — Oecologia 6: 318—327.

Turnbull, A. L., 1962. — Quantitative studies of the food of Linyphia triangularis Clerck (Araneae:

Linyphiidae). — Can. Ent. 94: 1233—1249.

, 1965. — Effects of prey abundance on the development of the spider Agelenopsis potteri

(Blackwall) (Araneae: Agelenidae). — Can. Ent. 97: 141—147.

Wiebes, J. T., 1959. — The Lycosidae and Pisauridae (Araneae) of the Netherlands. — Zool.

Verh. 42: 1—78.

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; No. 4. F. Willemse, 1968. — Preliminary revision of the genera Stenocatantops Dirsh & Uvarov

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No. 6. J. G. Betrem, 1971. — The African Campsomerinae (Hymenoptera, Scoliidae), 326 pp.,

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HYMENOPTEROUS PARASITES IN EGG SACS OF SPIDERS

OF THE GENUS PARDOSA (ARANEIDA, LYCOSIDAE)

A. KESSLER

Department of Biology, Free University, Amsterdam

and

A. FOKKINGA

Kolejy Loterana, Manantantely, Fort Dauphin, Madagascar

With 2 text-figures, 4 graphs and 3 plates

ABSTRACT

The occurrence of two hymenopterous egg parasites, Gelis spec. (Ichneumonidae) and Acolus

krygeri Kieffer (Proctotrupidae), in egg sacs of spiders of the genus Pardosa (Araneida, Lycosidae)

in the Netherlands is described.

Gelis spec. develops in the spider egg sac. All spider eggs are either eaten or destroyed by the

larvae. Only a small proportion of Pardosa egg sacs is parasitized by Gelis: © 140 out of + 5000

egg sacs. In some species and at some sampling sites the degree of parasitism can be rather high,

up to 42.6%.

Acolus krygeri develops in a single spider egg. Only a proportion of spider eggs in an egg sac

is parasitized, the other eggs develop into young spiderlings normally.

Acolus krygeri occurs in the Netherlands only on the Frisian island Schiermonnikoog. This species

parasitizes mainly egg sacs of Pardosa nigriceps (Thorell), viz., to about 70%, with a mean number

of 10 parasites per sac; this means that 30 to 60% of the spider eggs are attacked. To a lesser extent

egg sacs of P. pullata (Clerck) are attacked.

CONTENTS

Taro dnerio ni e ee OP a ta ea PERL ESS ©

Itife'historyiof®Purdosa'in.thie Netherlands’ . 4 62°. wu. 44

The ents. A ee ee eee ee EE ea 4

i Catene) Mme ANS SANE NL RA NEE ET MER ME A

Results nd As I ben a AED

MerGielisi spec. . ~ ER ee ee NE Be LES A 4S

A. Field dhectaliona ad Er A dem nd learn A

Number of larvae in Ne spider « CÉRISAC AS St in EEE dn le AG

B. Laboratory observations . . eat a tae fetes Gets. 71

Parasitismeok the spider ess sac he Ai IAN SEP) re Jagt 8

Development of Gelis larvae. . . SR re RT UE, AB

Behaviour of the spider towards the parasite Ee, Veen aries URN At sé 49

CONCLUS (ons N E TEA E cat ©

Discussion AREN e e el 20

2. Acolus krygeri . . EE Me CRE A SR I En ss ok os OM

A. Field pbsemations OD EEE OENE o Nt i ae a naro

44 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 3, 1973

Number of latvae/in the spider egaisae ) i 2

B. Laboratory observations |... Icons lan CM

Sex ratios lol en ed a O ST At

Parasitizing. of the egg:sac M Tens Re MAIN u ee

Development of the Acolusilatvae ds \. sea. apg na AR RDD

Number of larvae per female parasites OM NP RE EE SG

Actual time of thesparasitizingsinsthe field NN EE PE SC

Conclusions =... a NERO NC EN RE en. IN ED

Discussion: ar Ver i EEE EE ER TS

3. The occurrence of Acolus krygeri and Gelis spec. together. . . . . . . . . . . . 59

Conclusions SIRET RD EE GO

General, discussioni x. SAC OR RER CE AS ERGO

Acknowledgements 2202020 OO AR MON EN RI C0

References NN et DRE PL à CD

INTRODUCTION

In order to study the egg production of spiders of the genus Pardosa (Lycosidae) in

the field, a large number of female spiders carrying egg sacs have been collected. In

some samples a number of eggs sacs contained larvae of a hymenopterous parasite, Gelis

spec. (Hymenoptera, Ichneumonidae). In other samples, collected on the Frisian island

Schiermonnikoog, larvae of Acolus krygeri Kieffer (Hymenoptera, Proctotrupidae) were

found in spider eggs. A study of the interrelation between parasites and spiders was

initiated, in order to establish the effect of parasitism on egg production in spiders of

the genus Pardosa. The results of this study are presented in this paper.

Life history of Pardosa in the Netherlands

In early spring the juvenile spiders moult to the adult stage (March-April). About

one month later the females construct egg sacs, which are carried around on the

spinnerets (May-June). Again after about one month the juvenile spiders emerge. The

females can produce a second egg sac (July-August), and very seldom, a third one.

Most of the juvenile spiders reach the penultimate stage before winter. For more detailed

description of the life history of Pardosa may be referred to Vlijm et al. (1963).

Eight species of the genus Pardosa can be found in reasonable numbers in the Nether-

lands: P. amentata (Clerck), P. lugubris (Walckenaer), P. pullata (Clerck), P. prativaga

(L. Koch), P. nigriceps (Thorell), P. purbeckensis F.O.P.-Cambridge, P. monticola

(Clerck), and P. palustris (Linnaeus).

The parasites

As is said above, we have to deal with two types of egg parasites.

1. Gelis spec. (Hymenoptera, Ichneumonidae).

The members of the genus Gelis are ant-like insects; the females are wingless, the

males have wings; their length is 2 to 2.5 mm (PI. I Fig. A1 and A2). The species

are rather difficult to identify, and therefore they are dealt with as a genus. The larvae

develop in spider egg sacs in such a way, that no spiderlings can emerge from the

parasitized egg sac; the larvae consume all the spider eggs or, if not all eggs in the sac

are eaten, the remaining eggs are destroyed by the prepupae.

A. KESSLER & A. FOKKINGA: Parasites in Pardosa eggs sacs 45

2. Acolus krygeri Kieffer (Hymenoptera, Proctotrupidae, Scelioninae).

These are rather small insects (length + 1.2 mm). The females are wingless, the

males have wings (PI. I Fig. B1). The larvae develop in a single spider egg. Non-

parasitized spider eggs develop normally. The species was recorded by Kryger from

Denmark, obtained from eggs sacs of Lycosa spec., especially Lycosa picta (the latter is

probably synonymous with Arctosa perita Latreille).

MATERIAL AND METHODS

All samples of Pardosa females with egg sacs were collected by hand on sunny days.

In this way one only catches spiders, that are active upon the vegetation. However, there

is reason to believe that on sunny days nearly all females are out on the vegetation,

exposing their egg sacs to the sun.

The parasites used for experimental purposes were obtained by collecting Pardosa

females with egg sacs from localities, where in former years a reasonable number of

egg sacs were found to be parasitized. The spiders were kept in cages and as soon

as parasites emerged, these were transferred to small glass jars and supplied with water

and honey. The temperature was kept at 20 to 25°C.

Previously a number of Pardosa females were retarded in their development by keeping

them under low temperature conditions. Thus they constructed their first egg sac after

the emergence of the first egg sacs of spiders in the field, and just ín time to supply

the parasites in the experiments with fresh spider egg sacs.

RESULTS

1. Gelis spec.

A. Field observations

Larvae of Gelis spec. have been found in egg sacs of all Pardosa species in the

Netherlands, except in P. palustris.

In table 1 all available data are presented. It is evident from this table that the degree

of parasitism is highly variable among the different Pardosa species. In nearly 35% of

the samples Gelis larvae were found. The degree of parasitism of Gelis in Pardosa egg

sacs in general is not very impressive. Only 139 out of 5116 egg sacs were found to

be parasitized. On 65% of the sampling sites, however, we never found parasitized egg

sacs, even though a high number of sacs were collected on these sites.

When we consider the number of parasitized egg sacs in those samples where

parasites were found, it is evident that the degree of parasitism can be rather high

(Table 2). The highest parasitism (e.g. 42.6% in P. amentata) was found in samples

of second egg sacs. Moreover, in P. purbeckensis and P. pullata only the second egg

sac was found to be parasitized. It is not clear whether the first egg sac in these two

species is not parasitized at all. More likely the number of parasitized egg sacs is so

low, that they have not been met with in the samples. It should be noted that we did

not succeed in taking samples of second egg sacs of all species and on all sampling sites.

46 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 3, 1973

Table 1. General impression of the occurrence of Gelis larvae in egg sacs of species of Pardosa

at different sampling sites

Spider Number of Number of Number of samples Number of Total number

species egg sacs samples with parasitized sampling of parasitized

egg sacs sites egg sacs

P.amentata 1006 16 976.37) 6 53

P.lugubris 601 6 3 (50.07) 3 31

P.pullata 791 17 6065257) 2 13

P.prativaga 147 2 1 (50.0%) 2 12

P.nigriceps 1324 18 5 (27.82) 2 9

P.purbeckensis 609 11 2275) 3 20

P.monticola 445 7 I (14.32) 3 l

P.palustris 195 3 > È 2 =

Total 5116 81. 28 (34.6) 1200 139

Some sampling sites are the same for several species

Table 2. Mean percentage of parasitism in samples of Pardosa species, where Gelis larvae were

found

Mean % of Number

parasitized of samples Highest and

egg sacs lowest % found

P. amentata 9.7 9 42.6 — 0.7

P. lugubris 8.1 2 22.6 — 2.0

P. pullata 8.9 6 16.7 — 2.1

P. nigriceps 3.7 5 5.9 — 18

P. purbeckensis 14.7 2 25.7 — 3.7

P. monticola 2.0 1 2.0

P. prativaga 8.0 1 8.0

These considerations do suggest that Gelis presumably is much more widespread than

is indicated in table 1.

Number of larvae in the spider egg sac.

The interrelation between the number of spider eggs per egg sac and the number

of larvae of Gelis is shown in table 3. The size of spiders with parasitized egg sacs did

not differ from that of spiders with normal egg sacs. Thus there is no reason to assume

that the parasitized egg sacs contained different numbers of spider eggs, this number

being correlated with the size of the mother spider (cf. Petersen, 1950). Moreover, the

number of eggs could be counted when the Gelis larvae were very young, and this

A. KESSLER & A. FOKKINGA: Parasites in Pardosa eggs sacs 47

Table 3. Mean number of Gelis larvae per egg sac found in samples of the first (1) or second (2)

egg sac of different Pardosa species, and the calculated mean number of spider eggs available to one

Gelis larva in the different samples

Spider First or Mean number Mean number of Number of spider Number and percent-

species second of spider eggs Gelis larvae eggs available age of parasitized

egg sac per egg sac in parasitized to one Gelis egg sacs in the

egg sacs larva sample

P.pullata 2 16.0 TS IZ 8.9 6 (21.6)

P.purbeckensis 2: 26.7 SAM OE 8.6 1870261)

P.amentata 2 49.7 4.9 + 1.94 TO 23 (42.6)

P.lugubris 1 40.5 5.1 + 2.35 7.4 19 (22.6)

P.amentata 1 74.4 6.6 + 4.28 ito) 7X Wor)

P.prativaga 1 48.9 TION 237 6.4 12. (10.2)

P.amentata 2 54.1 160: 31110 Te 7 (13.0)

P.amentata 1 65.7. 10.3 + 3.24 6.4 87.089)

number did not differ from the numbers in non-parasitized egg sacs. However, as a rule,

it is not possible to count the number of spider eggs in a parasitized egg sac. Therefore

the mean number of spider eggs in not parasitized egg sacs of the same samples is

chosen as an estimate of the spider eggs available to the larvae in a parasitized egg sac.

There clearly is a relation between the number of host eggs and the number of Gelis

larvae. It is striking, that the number of larvae is highest, when the percentages of

parasitized egg sacs in the samples are lowest. This is, however, a consequence of the

fact, that second egg sacs, containing fewer eggs than the first egg sacs, have a higher

degree of parasitism. The number of eggs available to one Gelis larva ranges from

6.4 to 11.3.

Table 4. Mean number of old and young Gelis larvae per egg sac in one sample of Pardosa

lugubris and one sample of P. prativaga

Spider species Young larvae Number of Old larvae Number of

egg sacs or pupae egg sacs

P. lugubris A188 12 5.6 = 2.38 11

P. prativaga Gone 243 6 Vee) 6

In two samples of Pardosa lugubris and P. prativaga, collected in the same period,

it was possible to compare egg sacs with very young Gelis larvae (in that stage the spider

eggs are not yet damaged), with egg sacs containing old larvae or pupae. The results

are shown in table 4. The mean numbers of old and young larvae were not significantly

different in those samples. Therefore it may be concluded, that the number of Gelis eggs,

deposited in one egg sac, is proportional to the number of spider eggs in these egg sacs.

B. Laboratory observations

A number of spiders carrying egg sacs was collected in the field and kept in cages.

Every day the cages were searched for parasites. A total number of 49 specimens was

collected that way : 285 and 219 (Table 5). The slight predominance of males over

48 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 3, 1973

females is not statistically significant. The parasites were kept in glass tubes, together

with a small sponge soaked in water and honey.

After emergence the males and females mated very soon (duration of the copulation:

5-10 minutes); consequently, the females were able to lay eggs within 1 or 2 days

after emergence.

Table 5. The number of Gelis males and females emerged from different samples of Pardosa

amentata females with egg sacs, collected in the field

Spider species : Number of Total number of Gelis

egg sacs in the sample

P. amentata 8 9

30 4 6

90 10 5

70 7 3

11 4 3

40 3 4

28 21

Total

Parasitizing of the spider egg sac.

When a Pardosa spider carrying a fresh egg sac is put in a tube together with a

Gelis female, the latter becomes very active. After about 10 minutes the Gelis female

jumps on the egg sac, walks around on the surface of the egg sac for a few minutes

and then pierces the egg sac with her ovipositor (Pl. I Fig. B2). The eggs are mostly

deposited at the edge of the egg sac, where the two halves of the sac are joined together

(for a description of the egg sac, cf. Vlijm et al., 1963). After egg laying the Gelis

female leaves the egg sac or sometimes pierces the sac at another point. The number of

parasite eggs found in the egg sacs in these experiments varied between 1 and 7.

An easier method to obtain parasitized egg sacs is to remove the sac from the female

spider and put it in a tube with the parasite. It takes less time then for the parasite to

mount the egg sac than in the case of a spider running around with its egg sac. After

being parasitized, the egg sac be returned to the owner; in all cases it was readily

accepted by the female spider.

Development of the Gelis larvae.

The development of the larvae was studied by keeping larvae separately with some

spider eggs, which were replaced by fresh ones every two days, in “cages” (small glass

rings with some moist plaster of Paris on the bottom and sealed with a piece of filter

paper, Fig. 1). The results were compared with data of larvae developing normally

EE © ©

Fig. 1. Glass “cage” with one Gelis larva and some spider eggs

A. KESSLER & A. FOKKINGA: Parasites in Pardosa eggs sacs 49

within a spider egg sac. This procedure had to be followed since the Gelis larvae are

lost for the experiment when egg sacs are opened for inspection and determination of

the development of the larvae. Moreover, in the small cages one can easily assess the

feeding rate of the larvae.

In a temperature range from 20 - 25°C the total development took from 16 - 20 days.

The development of the spider eggs under these conditions takes about 20 - 25 days

(Table 6; PI. II). Only in the active larval stage spider eggs are eaten. This stage lasts

2-3 days. During this time the larvae consumes on the average 7 spider eggs (min.

5 eggs; max. 13 eggs). This is in agreement with data from the field samples

(Table 3).

The development of the larvae in the normal egg sacs and in the glass cages proved

to be the same under these temperature conditions. The larvae destroy all the spider

eggs in the egg sac. If not all eggs are eaten, the remaining eggs are smashed by the

prepupae. When the imago is ready to emerge it bites a hole in the wall of the egg

sac, or emerges out of holes bitten by the mother spider to release the juvenile spiders,

Table 6. Duration of the stages in the development of Gelis

Time in days Larval stage Size of the larva in mm

Ls) egg 0.5 x 0.1 PI. II Al

3 — 4 active larva OZONO Ee 04, PN II A?

5 active larva el x 0:4 sto 93.5 x 14m PID

6 full grown larva 3.5 x 14 PI. II B2

7, 8, 9, 10 prepupa (silkspinning) PI. II C1

10 — 16 — 20 pupa PI. II C2

16 — 20 imago

even though the latter are not present any more. This phenomenon has not yet been

studied in detail.

Behaviour of the spider towards the parasite.

When a Gelis female is sitting on a spider egg sac, the spider does not seem to

notice: it shows no reaction at all. When a spider meets a moving Gelis specimen

it is sometimes grabbed, but in all cases observed, the spider immediately released the

parasite undamaged. The spider takes care of a parasitized egg sac in a normal way,

even when it becomes seriously deformed when the larvae are in the pupal stage. Even

in the field one can easily recognize a parasitized egg sac at this stage.

Conclusions

1. On the whole the parasitism by Gelis is not very important in reducing natality

in Pardosa spiders: only 139 egg sacs out of 5116 contained Gelis larvae, Table 1.

However, in some localities and especially in the second egg sac it can be important; e.g.

42.6% of the egg sacs were found parasitized in a sample of the second egg sac of

Pardosa amentata, Table 3.

2. The number of parasites emerging from a spider egg sac is dependent on the

50 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 3, 1973

size of the egg sac; from 1.8 larvae in the second egg sac of Pardosa pullata, containing

16.0 spider eggs, up to 10.3 larvae in the first egg sac of Pardosa amentata, containing

65.7 spider eggs, Table 3.

3. The parasite adapts the number of eggs laid to the size of the spider egg sac;

regulation of the numbers of parasites is therefore determined by the female parasite

and not by competition between larvae (conclusion 2 and table 4).

4. The ratio 4/2 does not differ statistically from 1.

5. It is possible, at least under laboratory conditions, to raise the larvae of Gelis

to the adult stage outside the spider egg sac, provided enough food is presented in the

form of spider eggs.

6. A Gelis larva needs about 7 eggs of a Pardosa spider to complete its devel-

opment, under laboratory conditions. In the field the spider eggs available to a single

Gelis larva range from 6.4 to 11.3

7. The development of Gelis from egg to the adult stage takes about the same

time as, or is somewhat shorter than, the development of the spider eggs into juvenile

spiders.

8. No conclusions can be drawn on the hibernation of Gelis spec.

Discussion

A number of authors have described the occurrence of Gelis spec. in egg sacs of

several spider species. A list of reference on all spider parasites is given by Eason et al.

(1967). They state that the records of spider parasites mainly consists of brief and

incomplete accounts. More recently, Horstmann (1970) extensively studied the ecology

of Ichneumon flies in Schleswig-Holstein. He described two species of Gelis, G. micrurus

and G. pumilus, both parasitizing egg sacs of Linyphiid spiders, while G. micrurus also

parasitizes Pardosa egg sacs. Both species have more than one generation per year. Gelis

micrurus parasitizes Linyphiid egg sacs, when Pardosa egg sacs are not available any

more. In Linyphiid egg sacs there is one larva (Solitärparasit), whereas in Pardosa

egg sacs there are more than one (Gregärparasit).

In our study no separate species of Gelis are distinguished. It is possible, that some

of the differences found must be ascribed to specific differences. The mean number of

spider eggs and the mean number of Gelis larvae per egg sac were calculated for each

sample of egg sacs. A positive correlation between the mean number of these eggs

and mean number of Gelis larvae per sac was demonstrated in comparing all samples

of Pardosa egg sacs. Within a sample, however, no correlation between size of the egg

sac and number of Gelis larvae was found. It is possible to estimate the original number

of spider eggs in the parasitized egg sac by the size of the corresponding spider. This

might mean that in different Pardosa species and in different localities, we are dealing

with different Gelis species or subspecies, adapted to the size of the spider egg sac

which is normally available to them. However, from laboratory experiments there is an

indication that Gelis individuals bred from egg sacs from one locality and sampled at

the same time, deposit more eggs in Pardosa amentata egg sacs, with a high number of

eggs, than in Pardosa monticola egg sacs, with a much lower number of eggs.

The observation of Horstmann that the larvae of Gelis micrurus are solitary in the

small Linyphiid egg sacs and gregarious in Pardosa egg sacs points in the same direction.

As indicated by Horstmann, Gelis micrurus parasitizes Linyphiid egg sacs when Pardosa

A. KESSLER & A. FOKKINGA: Parasites in Pardosa eggs sacs 51

egg sacs are not available. It is not clear whether one generation of Gelis micrurus

parasitizing Linyphiid egg sacs and the other generation(s), Pardosa egg sacs, or whether

there is a gradual shift to other egg sacs.

In this context it is of importance to study the behaviour of Gelis spec. in connection

with egg sacs of other spider species.

2. Acolus krygeri Kieffer

A. Field observations

As already remarked above, Acolus krygeri has been found in the Netherlands only

on the Frisian island Schiermonnikoog; samples from other Frisian islands were not

available and our observations therefore only refer to Pardosa species found on that

island : P. nigriceps, P. pullata, P. purbeckensis and P. monticola.

Acolus krygeri is practically restricted to P. nigriceps and P. pullata as host species

(Table 7A). It is seldom found in egg sacs of P. monticola and P. purbeckensis (Table

7B). Acolus seems to be restricted to the typical habitat of P. nigriceps on Schier-

monnikoog. This is a dense vegetation of Carex arenaria and Salix repens in a dune area

Table 7A. Occurrence of Acolus larvae in egg sacs of Pardosa species. Samples from the habitat

of P. nigriceps

Pardosa species First (1) or Number of Parasitized

second (2) egg sacs egg sacs %

egg sac

P. nigriceps 1 359 227 63.2

P. nigriceps 2 801 564 70.5

P. pullata 1 22 10 45.5

P. pullata 2 124 57 46.0

Table 7B. Occurrence of Acolus larvae in egg sacs of Pardosa species. Samples from the typical

habitat of the spider concerned

Pardosa species First (1) or Number of Parasitized %

second (2) egg sacs egg sacs

egg sac

P. pullata 1 146 11 7.5

P. purbeckensis 1 97 4 4.1

P. monticola 1 50 6 12.0

(Vljm & Kessler-Geschiere, 1967). The data in Table 7A refer to specimens found in

this habitat. The data in Table 7B are based on specimens sampled in other habitats,

mostly bordering on the habitat of P. nigriceps. The data in Table 7 are based on

samples from several places on Schiermonnikoog and from several years.

Table 8 shows the percentages of parasitism in 1968 and 1969 at the same sampling

site, both for the first and second egg sacs.

Table 9 shows the differences in percentage of parasitism between sampling sites in

1968 for the second egg sac.

Because of the small numbers of P. pullata found in the samples (habitat of

P. nigriceps!), this could be done only for P. nigriceps. It is clear that there are no

52 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 3, 1973

conspicuous differences in percentages of parasitism, neither between the first and

second egg sacs nor in the different localities (sampling sites). These data are confirmed

by additional samples of either the first or the second egg sac of P. nigriceps from

other years.

Number of larvae in the spider egg sac.

Although in several egg sacs all spider eggs were parasitized, this generally is the

case with only a portion of the eggs. The non-parasitized eggs develop into young

spiderlings in a normal way.

There is a relation between the size of the spider egg sac and the number of parasites

found (Table 10), which is especially clear for the second egg sac. It is striking, that

Table 8. Differences in percentage of parasitism in egg sac samples of Pardosa nigriceps on the

same sampling site in 1968 and 1969

First egg sac Second egg sac

N % N %

1968 85 63.5 70 78.6

1969 5 64.2 21 61.9

although the mean number of spider eggs in the first egg sac is much higher than in

the second, the mean number of parasites is the same for both egg sacs: about 10. This

means that in the first egg sac about 30% of the spider eggs is parasitized, whereas

in the second egg sac this percentage is about 60% (Table 11). This is also found

for egg sacs of Pardosa pullata (Table 11), although the percentage of parasitism in

the samples is much lower here: about 45% (Table 7A). If we compare all samples

of second egg sacs of Pardosa nigriceps with a degree of parasitism lower than 70%,

with the samples where the percentage of parasitism is higher, we see that a lower

percentage of parasitism results in a lower mean number of parasites per egg sac

(Graph 1).

Fig. 2. First stage larva of Acolus krygeri

However, the difference is not very conspicuous. The number of parasites in parasitized

egg sacs ranges from 1 to 42. The frequencies are given in Graph 2. It is clear from this

figure, that the same mean number of parasites in the first and second egg sac is reached

A. KESSLER & A. FOKKINGA: Parasites in Pardosa eggs sacs 53

Table 9. Differences in percentage of parasitism in the second egg sac of Pardosa nigriceps on

several sampling sites

Sampling site Number of egg sacs Percentage of

parasitized egg sacs

1 70 78.6

2 60 60.0

3 47 76.1

4 30 70.0

5 54 77.8

6 51 74.5

7 55 69.1

8 41 82.9

9 41 92.9

Table 10. Relation between size of the egg sac (number of eggs per egg sac) and the number of

parasites per egg sac for Pardosa nigriceps; A, data on first egg sac, B, second egg sac

size of the 4-6 7-9) 210-172) 3132157 N6=18 19-21 22-24 25-27 28-30 31-33 34-36 37-39 40-42 43-45 46-48

egg sac (number

of spider eggs)

mean number of ‘

parasites per 7.8 10.6 8.0 923 9.8 10.8 976 1223) 12.8 23.4

egg sac

N 5 10 27 42 54 38 28 12 6 5

Z parasitized

eggs in the egg 39.0 46.0 30.8 32.1 30,6 30.9 2563 30.0 28.8 49,8

sac

mean number of

parasites per Sa E58 6.6 8.7 10.4 1189) 1491 1553 16.0

egg sac

N 5 12 60 114 151 117 70 26 8

% parasitized

egestinethevege. 72.0, 72.5 660.0) 62,24 61.2 59.5 61.3 58.8 55.2

sac

Table 11. Mean number of spider eggs and mean of Acolus larvae per egg sac in first and second

egg sacs of Pardosa nigriceps and Pardosa pullata from one sampling site

Host species First or N Mean number of Mean number of N % of parasitized

second spider eggs in parasites in para- eggs in the egg

egg sac the egg sac sitized egg sacs sac

P.nigriceps i 359 32 ONE MOON 9.9 + 6.94 227 30.9

P.nigriceps 2 801 17.0 + 4.65 104 + 5.67 564 61.2

P.pullata 1 2 DMN ONORE 5565 OA RE EU 10 35.6

_P.pullata 2 124 RES 8.6.4 5.59 57 50.6

54 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 3, 1973

freguency

0.200

0.100 /)

ERS

lina...

1-3 4-6 7-9 10-12 13-15 16-18 19-21 22-24 25-27 28-30

number of parasites

Graph 1. Frequency distributions of number of parasites (Acolus) per egg sac in samples with a

degree of parasitism less than 70% (white: N = 183; M = 9.2 + 5.76) and samples with a

higher degree of parasitism (hatched: N = 894; M = 11.0 + 5.54)

in a similar way. It seems that it is not so much dependent on the size of the egg sac,

but on other phenomena. In Graph 3 the frequencies of the parasitized egg sacs are

compared with the frequencies of the total number of parasitized and non-parasitized

egg sacs together. Within the groups of first or second egg sacs there is an even chance

for every egg sac, not dependent on size, to become parasitized. Acolus, therefore, does

not seem to discriminate between large and small egg sacs.

In about 20 cases a spider egg appeared to contain 2 larvae of Acolus, this is a very

low percentage: about 0.5%.

Laboratory observations

Sex ratio.

To determine the sex ratio of Acolus two samples of Pardosa nigriceps second egg sacs

were collected in the field. The spiders with egg sac were kept separately in glass tubes.

After emergence the parasites were collected and counted. The results are shown in

table 12. There is a dominance of females over males. This ratio fluctuates when we

consider the numbers of parasites emerging from an egg sac. When there are only a few

parasites in the egg sac the males predominate (Table 13).

Mating occurs within a day after emergence. The parasites were provided with water

and honey; it is not clear whether the females need food to develop the eggs. In other

experiments, where no honey or sugar were provided the females were able to parasitize

spider eggs succesfully.

Parasitizing of the egg sac.

A female spider with a fresh egg sac was put in a glass tube, together with some

female Acolus specimens, which had already mated. When the egg sac comes in reach

of the parasite, the animal takes a crouching position with bent hind legs. This reaction

can also be provoked by approaching the animal with the tip of the finger or a pencil.

A. KESSLER & A. FOKKINGA: Parasites in Pardosa eggs sacs 55

It then jumps on the egg sac and walks around, tapping the surface of the egg sac with

the antennae. Every now and then it stops and pierces the egg sac with the ovipositor

(PI. III Fig. A1). The length of the ovipositor is only 0.4 mm, the spider eggs have

a diameter of 1 mm or more, consequently only spider eggs at the surface of the egg sac

Table 12. Number of males and females of Acolus emerged from egg sacs of Pardosa nigricebs

Sample Number of Number of Number of Ratio 3/9

egg sacs males females

1 28 105 212 0.495

2 20 49 105 0.467

are within reach of the parasite. After 10-30 minutes the parasite leaves the egg sac

and walks around in the glass tube, after which it may again jump on the egg sac. This

is the more easily observed when the egg sac is removed from the female spider and thus

stays in the same place. i

In this way egg sacs of Pardosa nigriceps as well as those of Pardosa amentata were

succesfully parasitized. All egg sacs less than 5 days old, were succesfully parasitized;

in two cases where the parasite was apparently parasitizing egg sacs of 7 and 10 days

old, no parasites emerged.

Development of the Acolus larvae.

The embryonic development of the parasites was studied by immersing the parasitized

spider eggs in paraffin oil, following the technique by Holm (1940) for observing the

development of living spider embryos. The egg membrane becomes transparent which

makes the larvae of the parasite easily visible.

Controls were made by opening parasitized spider egg sacs of the same age and

studying the parasitized eggs in alcohol. The paraffin oil proved to have no effect on

the embryonic development of the larvae. At temperature conditions of 25°C the total

development took 18-21 days in the following scheme:

day 1 - 3 egg stage

day 4 Ist stage larva pl 1 Az

day 5 2nd stage larva pl. III B1

day 6 - 7 3d stage larva (prepupa) pl. III B2

day 8 - 21 pupa

During the first 3 days no details in the development of Acolus could be observed

with the techniques used. The first stage larvae have a curious shape (Fig. 2), probably

adapted to floating in the fluid of the spider egg. The active larval stage takes only

two days, during which time most of the contents of the spider egg are eaten by the

larva. After this active stage the larva becomes immobile; then follows the prepupal

and pupal stages in which no clear observations on the development could be made. The

longevity of the adult under laboratory conditions was about 14 days.

The influence of different temperatures upon the length of the larval development

is shown in table 14. Compared with the development of the spider embryos the

development of Acolus is short. The total number of parasites out of 20 experimental

egg sacs was 174, a mean of 9.1 parasites per egg sac.

56 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 3, 1973

frequency

0.200 A

0.100 M = 9.9

0.200

0.100 M = 10.4

Ie:

1-3 4-6 7-9 10-12 13-15 16-18 19-21 22-24 25-27 28-30 31-33 34-36 37-39 40-42

number of parasites

Graph 2. Frequency distributions of the number of parasites per egg sac in A : the first egg sac

and B : the second egg sac of Pardosa nigriceps

Number of larvae per female parasite.

To learn about the egg-potential of Acolus, 35 female spiders with a fresh egg sac

were put separately in glass tubes, each with a female Acolus. This resulted in a mean

number of 11.7 parasites per egg sac emerging from 35 egg sacs (minimum 1, maximum

28). The mean number of spider eggs in these egg sacs was 16.4. The frequency is

shown in Graph 4.

Actual time of parasitizing in the field.

During the period of time when female Pardosa nigriceps construct egg sacs some

samples were taken to determine the actual time of parasitizing of the egg sacs in the

field. Table 15 gives the results. On June 2, when only a fraction of the spiders had

their egg sacs already constructed, the percentage of parasitism was relatively low. Very

soon afterwards the percentage of parasitism reached a maximum. The mean number

of parasites per egg sac in the samples was fairly constant.

A. KESSLER & A. FOKKINGA: Parasites in Pardosa eggs sacs 57

frequency

0.200

0.100 7

| In,

13-15 16-18 19-21 22-24 25-27 28-30 31-33 34-36 37-39 40-42 43-45 46-48

0.300

0.200

0.100 /

1-3 4-6 7-9 10-12 13-15 16-18 19-21 22-24 25-27 28-30

number of eggs per egg sac

Graph 3. Frequency distributions of number of eggs per egg sac: white: parasitized and not-

parasitized egg sacs together, hatched : parasitized egg sacs; A = first egg sac, B = second egg sac

; of Pardosa nigriceps

Conclusions

1. The occurrence of Acolus krygeri on the Frisian island Schiermonnikoog is prac-

tically restricted to the habitat of Pardosa nigriceps: low dunes with a dense vegetation

of Carex arenaria.

2. In this habitat Acolus is able to parasitize both the first and second egg sacs of

P. nigriceps for about 70%. For the second egg sac of P. pullata this percentage is only

about 45%.

3. The mean number of parasites in a parasitized egg sac is about 10. This means that

58 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 3, 1973

in the first egg sac of P. nigriceps about 30% of the spider eggs in a parasitized egg

sac contain larvae of Acolus, in the second egg sac this percentage is about 60%.

4. Asa result of parasitism the first egg sac of P. nigriceps yields on the average

about 75% of the potential number of spiderlings. For the second egg sac this per-

centage is about 60%.

Table 13. Ratio 4/9 arranged following the number of specimens emerging from one egg sac.

The samples are the same as in table 12

Number of parasites Sample 1 N Sample 2 N

emerging ratio 3/9 ratio 3/9

1— 5 1.667 26 0.941 33

6 — 10 0.238 8 0.889 17

LI — 15 0.427 157 0.327 65

16 — 20 0.537 126 0.300 39

Discussion

Although there is a wider range of data on Acolus krygeri, the relationship between

Acolus and Pardosa remains obscure. No data on the relation between Acolus and

Pardosa are available in literature. It is not clear in the first place whether an egg sac

is parasitized only once or more than once by one or by more females of Acolus.

Considering the results shown in Graph 4 it is evident that one female Acolzs is able to

lay up to 28 eggs (in other experiments even 44 eggs) in one egg sac, but in some

cases it parasitizes not more than a single spider egg in an egg sac. These data can

explain the wide range of number of parasites per egg sac found in the field.

Table 14. Length of development of Acolus larvae under different temperature conditions

Temperature Length of development in days

20°C 25 — 28

252C 18 — 21

30°C 12 — 14

354€ 8

Parasites apparently may discriminate (cf. Salt, 1936) between parasitized and un-

parasitized hosts. If this is true for Acolus then the parasite may consider an egg sac

with some parasitized eggs unsuitable and pay no further attention to it. However,

it is also possible that the parasite distinguishes only between parasitized and non-

parasitized eggs. In that case an egg sac with a few parasitized eggs can be parasitized

again by another parasite.

If egg sacs can be parasitized more than once, this may be expected to happen

especially when the density of parasites is highest. The data in Graph 1 suggest that in

samples with a high degree of parasitism, probably due to a high density of parasites,

the egg sacs are parasitized more often than in samples with a relatively low percentage

of parasitism. This results is a higher mean number of parasites per egg sac in the

former case.

Another problem arises from the fact that sometimes all or nearly all spider eggs in

A. KESSLER & A. FOKKINGA: Parasites in Pardosa eggs sacs 59

an egg sac are parasitized. The length of the ovipositor is only 0.4 mm, while the

spider eggs measure at least 1 mm. If the eggs are laid directly in the spider eggs, only

eggs near the surface of the egg batch can be reached. There are, however, so many egg

sacs with all spider eggs parasitized (in the second egg sac of P. nigriceps in about 5%

frequency

0.200

0.100

1-3 4-6 7-9 10-12 13-15 16-18 19-21 22-24 25-27 28-30

number of parasites per egg sac

Graph 4. Frequency distribution of number of parasites per egg sac (explanation in text)

of all the cases all eggs are parasitized; in about 10% of the cases all eggs minus 1

are parasitized), that another possibility must be thought of. The explanation might be

that the ovipositor is extendable during egg-laying. Or the parasite eggs are laid in or on

the egg sac and the larvae crawl inside the egg sac and so settle in a single egg. This

latter assumption, however, is highly improbable. In the laboratory experiments the

spider eggs were removed from the egg sac immediately after parasitizing and put in

paraffin oil. Nevertheless these eggs produced full-grown parasites.

When all samples are considered together, no distinct differences in mean number

of parasites per spider egg sac become apparent. No simple explanation can be given for

this. We know that the population of parasites is able to attack 60-80% of the

spider egg sacs, while they deposite on the average 10 eggs in an egg sac. Furthermore

there is evidence, both from field and laboratory observations, that Pardosa egg sacs can

only be parasitized when they are not more than a few days old. Probably the period

during which spider eggs can be parasitized is the limiting factor. However, it cannot

yet be understood how this operates in detail.

More data on density of host and parasite are not yet available. In this context it is

60 TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 3, 1973

Table 15. Percentage of parasitism of Pardosa nigriceps egg sacs by Acolus. The samples were

taken on the same sampling site

Date Sample size Number of parasitized Mean number of parasites

egg sacs per parasitized egg sac

(between brackets: %)

2-6-70 23 7 (30.4) 9.9 = 7.95

4-6-70 14 9 (64.3) 8.45 E25

5-6-70 25 16 (64.0) 10.3 = 5.19

9-6-70 17 13 (76.5) 12.9 = 7.66

15-6-70 41 29 (70.7) 11.1 = 8:07

important that the locomotory activity of female Pardosa after egg sac construction is

considerably lower than before (Vlijm & Richter, 1966).

Eason et al. (1967) describe an egg parasite: Idris spec. (Hymenoptera, Scelionidae)

reared from Pardosa lapidicina egg sacs.

The incidence of parasitized eggs in the egg sacs ranged from 63% to 94%, an

average of 28 parasites per egg sac, which averaged 35 spider eggs. The parasites only

attacked egg sacs that were less than 72 hours old and could not be induced to oviposit

in a second egg sac. Moreover this parasitie could not be induced to oviposit in the egg

of any spider other than Pardosa lapidicina, not even in those of its congener, P. milvina.

The larval development of the parasite took 21 to 22 days, which coincided with the

length of time that the eggs and first instar spiderlings of Pardosa lapidicina remain in

the egg sac. The parasites were dependent on the female spider as it had to open the

egg sac, otherwise the parasites could not emerge. The authors state: “Presumably most

or all of the eggs on the periphery of the mass, those that touch the egg sac covering

are parasitized, and those in the centre are spared probably due to the limitation in

length of the parasite’s ovipositor”.

Although there is a general resemblance with our observations on Acolus krygeri,

there are many differences. A coincidence is that Idris spec. as well as A. krygeri in

general do not parasitize all spider eggs in an egg sac. Eason (1966) established that

the female Pardosa lapidicina tends to destroy her egg sac at the end of the incubation

period if no living spiderlings are ready to emerge. In that case it is important for the

parasite to leave part of the spider eggs untouched.

The behaviour of Pardosa nigriceps and P. pullata towards their egg sac seems to be

different from that of P. lapidicina. If no living spiderlings emerge at the proper time,

the egg sac is abandoned; the parasites can emerge then by biting holes in the wall of

the sac.

3. The occurrence of Acolus krygeri and Gelis spec. together

In 1968 a number of egg sacs were collected, that contained Acolus krygeri and Gelis

spec. together. In total 15 egg sacs (9 of P. nigriceps and 6 of P. pullata) contained

Gelis larvae. Ten of these (66.7%) contained both Gelis and Acolus larvae. The mean

number of Gelis larvae per egg sac was 1.9, the mean number of Acolus larvae was

11.5. In the egg sacs with Gelis larvae alone the mean number of larvae was 2.2. No

spiderlings were found in the egg sacs. As indicated before, the mean number of larvae

in egg sacs with Acolus alone is about 10.

A. KESSLER & A. FOKKINGA: Parasites in Pardosa eggs sacs 61

Conclusions

1. In the group of egg sacs parasitized by Gelis the percentage of parasitism by

Acolus is comparable with the percentage of parasitism in the whole of egg sacs. This

means that Gelis is not able to recognize an egg sac already parasitized by Acolus, or

vice versa.

2. It seems that the larvae of Gelis cannot consume spider eggs already parasitized

by Acolus, for when there were spider eggs left in the sacs, these were in all cases

parasitized by Acolus.

GENERAL DISCUSSION

Some aspects of the biology of both parasites (Gelis and Acolus) had little or no

attention in our studies. Problems of hibernation, density and the successive generations

have not been dealt with. “The wealth of material concerning spider parasites is

composed principally of brief and incomplete accounts which are widely scattered in

the literature” (Eason et al., 1967).

The present study as a whole can be seen as an attempt to study the relation between

egg parasites and spiders more closely. This is only possible when there is at least a

substantial knowledge about the biology of one of the partners in this relationship. In

our department much work has been done on the biology of Pardosa spiders, and there-

fore, from our knowledge of spider species, we gained some insight in the biology of

the parasites. It is evident that knowledge about spider parasites may help to understand

the biology of the spiders.

ACKNOWLEDGEMENTS

We wish to thank Prof. Dr. L. Vlijm for his critisism and help during the

investigations and in preparing the manuscript; to Mrs. M. Giardina-Wind we are

indebted for investigating numerous egg sacs; to all participants of our field courses

on Schiermonnikoog for their help; to Mr. G. W. H. van den Berg, for drawing the

figures; to Mr. J. H. Huysing, for the photographs and to Miss Y. J. Weber, for

typing the manuscript.

REFERENCES

Eason, R. D., 1966. — Life history and behaviour of Pardosa lapidicina Emerton (Araneida:

Lycosidae). — Unpublished thesis. University of Arkansas.

Eason, R. R., W. B. Peck & W. H. Whitcomb, 1967. — Notes on spider parasites, including a

reference list. — Journ. Kansas Ent. Soc. 40 (3): 422—434.

Holm, A., 1940. — Studien über die Entwicklung und Entwicklungsbiologie der Spinnen. — Zool.

Bidr. Uppsala 19: 1—214.

Horstmann, K., 1970. — Ökologische Untersuchungen über die Ichneumoniden (Hymenoptera) der

Nordseeküste Schleswig-Holsteins. — Oecologia (Berlin) 4: 20—73.

Petersen, B., 1950. — The relation between size of mother and number of eggs and young in some

spiders and its significance for the evolution of size. — Experientia (Basel) 6: 96—98.

Salt, G., 1936. — Experimental studies in insect parasitism IV. The effect of super parasitism on

populations of Trichogramma evanescens. — Journ. exp. Biol. 13: 363.

Vlijm, L., A. Kessler & C. J. J. Richter, 1963. — The life-history of Pardosa amentata (Cl.)

(Araneae, Lycosidae). — Ent. Ber. 23: 75—80.

Vlijm. L., & C. J. J. Richter, 1966. — Activity fluctuations of Pardosa lugubris (Walck.) (Araneae,

Lycosidae) during the breeding season. — Ent. Ber. 26: 222—230.

Vlijm, L. & A. M. Kessler-Geschiere, 1967. — Phenology and habitat in Pardosa monticola, P.

nigriceps and P. pullata (Araneae, Lycosidae). — Journ. anim. Ecol. 36: 31—56.

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TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 3, 1973 Plaat 1

Plate 1. Hymenopterous parasites from Pardosa egg sacs. A 1, Gelis sp. male: A 2, Females of Gelis

sp.; B 1, Acolus krygeri, male and female; B 2, Female Gelis parasitizing an egg sac

A. KESSLER & A. FOKKINGA: Parasites in Pardosa eggs sacs

TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 3, 1973 Plaat 2

Plate 2. Development of Gelis sp. larvae. 1 A, Spider egg with two Gelis eggs; 2 A, 1B, 2 B,

Successive stages of active Gelis larva; 1 C, Prepupa; 2 C, Gelis pupae inside a spider egg sac, the

covering of the egg sac is partly removed

A. KESSLER & A. FOKKINGA: Parasites in Pardosa eggs sacs

TIJDSCHRIFT VOOR ENTOMOLOGIE, DEEL 116, AFL. 3, 1973 Plaat 3

Plate 3. Acolus krygeri. 1 A, Female parasitizing a spider egg sac; 2 A, First stage larva of Acolus

inside a spider egg; 1 B, Second stage larva of Acolus 2 B, Prepupa of Acolus

A. KESSLER & A. FOKKINGA: Parasites in Pardosa eggs sacs

h No. 4. F. Willemse, 1968. — Preliminary revision of the genera Stenocatantops Dirsh & Uvarov

and Xenocatantops Dirsh & Uvarov (Orthoptera, Acridiidae Catantopinae), 77 pp., 1 map, 6 pl.

| D.FI. 25.—.

È No. 5. C. A. W. Jeekel, 1970. — Nomenclator generum et familiarum Diplopodorum, 412 pp.

_ D.FI. 100—.

| No. 6. J. G. Betrem, 1971. — The African Campsomerinae (Hymenoptera, Scoliidae), 326 pp.,

= 47 figs., 6 pls. D.Fl. 120.—.

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