Prey and Periodicity of ramulosa1 (McCook) in Alfalfa2

KENNETH V. YEARGAN' Entomology Department, University of California, Davis 95616

ABSTRACT Visual observations of predation by Pardosa ramu/osa (McCook) in alfalfa fields indicate that Hemiptera, Diptera, and Araneae are important prey of this wolf . Time-sort pitfall trapping showed that P. ramu/osa and some of its more frequently taken prey species are primarily active during the day. Population samples of the predator and prey species were taken to ascertain seasonal relationships.

In contrast to the numerous studies of predaceous alfalfa fields in the summer. Such cracks are often insects in agro-ecosystems, there have been rela- used for escape by P. ramu/osa when disturbed, and Downloaded from https://academic.oup.com/ee/article/4/1/137/2395486 by guest on 27 September 2021 tively few analyses of the role of as preda- make the capture of feeding spiders more difficult. tors. Although spiders are frequently mentioned as Observations were made by moving systematically potential predators of insects, data on their prey and as stealthily as possible through the study area species are scarce. The occasional field observations taking care not to move through the same area of predation by spiders noted in the literature are twice on a given date. By bending or squatting near often mentioned merely as an aside to other work. the ground, it was possible to determine whether Representative of the few extensive field investiga- or not an individual of P. ramu/osa was feeding. tions of spider prey to date, Turnbull (1960) and When a feeding individual was observed, a metal Kajak (1965) studied the prey caught under natural cylinder (6 in. diam, 4 in. high) was gently lowered conditions by certain web-building species, and Edgar over it to prevent escape. A small aspirator was (1969), Hallander (1970), and Kiritani et al. (1972) used to capture the spider and its prey which were reported their observations of predation by certain placed in alcohol for identification of prey, aging species of wolf spiders. and sexing of predator, etc., in the laboratory. This study, conducted in alfalfa fields near Davis, Pitfall traps used for diel periodicity studies were Calif., during the 1972 and 1973, focused on the of the clock-driven model designed by Williams determination of the prey of the , Par- (1958) and modified by Nicholls (1970). Offset dosa ramu/osa (McCook), which is the most abun- funnels with a 13-in. diam opening were used. A dant species of spider in northern California alfalfa 1;2 -in. flange was placed around the inside perimeter fields (Yeargan and Dondale 1974). Although its of the funnel opening to prevent escape of organisms cryptic coloration, fast movement, and ground- which had fallen into the funnels. Funnels were dwelling habits made observation difficult, consider- polished regularly with silicone lubricant to further able qualitative information on the prey of P. ramu- reduce chances of escape. Preservative used in the /osa was obtained by visual methods. collection cups was ethylene glycol. Three traps The diel activity periodicities and seasonal abun- were placed ca. 100 ft apart near the center of a dance of P. ramu/osa and its observed prey species 100-acre alfalfa field. The traps were used during were investigated to better understand their biotic the period between irrigation and cutting (2-3 wk) relationships. Die! periodicities were determined by each month from June through October, 1973. Care means of time-sort pitfall traps similar to those util- was taken not to trample the vegetation during the ized for this purpose by Dondale et al. (1972). daily servicing of the traps. Although careful at- Population samples of predator and prey species tention was given to dust and moisture problems in were taken throughout the year to ascertain seasonal the turntable mechanism of the traps, some malfunc- relationships. Knowledge of these biological param- tioning was unavoidable. Malfunction during any eters allows a more meaningful interpretation of the part of the 24-h cycle constituted failure of that trap predation observations. for that date. An average of slightly over 2 traps per day functioned properly during the study. Each Procedure and Materials 24-h collection fell automatically into 6 time periods: Observations of predation were made between 8 4 AM-7 AM; 7 AM-12 noon; 12 noon-5 PM; AM and 6 PM, PDT, at about monthly intervals 5 PM-8 PM; 8 PM-12 mdnt.; 12 mdnt.-4 PM, following cutting and irrigation. The alfalfa was PST. short enough (4-8 in.) at this time to allow rela- To determine seasonality of predator and prey tively easy observation of ground-dwelling arthro- populations, samples were taken throughout the year pods, and as the soil was still moist, it lacked the at ca. 2- to 3-wk intervals with the D-Vac® suction numerous cracks characteristic of dry California device (Dietrick et al. 1959). Sampling dates were concurrent with the observation dates during the season when predation observations were made. Each I Araneae: Lycosidae. • Received for 'publication 24 June 1974. sample unit consisted of 20 I-ft' "suctions" taken 3 Present address: Dept. of Entomology, Univ. Kentucky, Lexington 40506. several feet apart along a 100-150-ft transect. On

137 138 ENVIRONMENTAL ENTOMOLOGY Vol. 4, no. 1 each sampling date 12 such units were taken along (e.g., Chloropidae) were abundant in alfalfa, they parallel transects which were ca. 50 ft apart. Bags were seldom observed as prey. containing the samples were placed in cold ice Pardosa ramll/osa appears to feed more often on chests in the field and returned to the laboratory. members of its own species than on other species After 3-4 h of further cooling at ca. 4.4°C, the of spiders in alfalfa. The category "unidentified" samples were processed in modified Berlese funnels under Araneae in Table 1 consists of specimens too similar to those described by Dietrick et al. (1959). damaged to be identified beyond order level. The only orthopteran prey observed were small Results nymphs of the common field cricket, Achaeta as- Observed Predation simi Ius Fab. Coleopteran prey consisted of adult and larval staphylinids, larvae of Collops vittatus The results of field observations of predation by (Say), and larvae of Hypera brunneipennis (Bohe- P. ramulosa are summarized in Table 1. The orders man) . Hard-bodied adult beetles were never ob- Downloaded from https://academic.oup.com/ee/article/4/1/137/2395486 by guest on 27 September 2021 Hemiptera, Diptera, and Araneae were represented served as prey, and the only certain observation of in ca. 78% of the 331 total observations. rejection of any captured prey item in the field was Leafhoppers constituted the highest percentage of that of an adult of H. brunneipennis. Despite their the homopteran prey. Several species of leafhoppers abundance in alfalfa, Lepidoptera and Hymenoptera were present, but the most common species, Acerata- appeared to constitute only a small fraction of the gallia obscura Oman, was by far the most frequently diet of P. ramu/osa. The only observed feedings on taken. Acyrthosiphon pisum (Harris) was the only Lepidoptera were one adult moth and 3 small larvae. aphid species observed as prey, and with the excep- Two observations of feeding on small parasitic adult tion of one nymph, only winged adult specimens Hymenoptera represented less than 1% of the total were taken by P. ramu/osa. Geocoris spp. (primarily observations. G. atric%r Montandon) constituted ca. 76% of the heteropteran prey, with other lygaeids and one Nabis Die! Periodicity sp. nymph representing the remaining 24%. The diel periodicity of P. ramulosa and other Most of the dipteran prey were small flies (less in alfalfa are presented in Fig. 1-11. than 4 mm long) belonging to the family Ephydridae. Since the 6 time periods used were of unequal Although other families of comparable-sized flies lengths, the numbers caught were converted to a

Table I.-Prey taken by Pardosa ramulosa in alfalfa fields, Yolo Co., Calif., 1972-73.

Number of observations per prey taxon May June July Aug. Sept. Total Prey taxa 1973 1973 1972/1973 1972/1973 1972 1972-73 Hemiptera Homoptera Cicadellidae 0 0 18/15 10/18 3 64 Aphididae 0 0 0/13 1/2 0 16 Heteroptera Geocoris spp. 0 3 1/14 3/ 7 1 29 Other 0 0 3/ 1 3/ 0 2 9 Diptera 1 40 2/17 2/9 2 73 Araneae Pardosa ramulosa 0 22 1/9 1/5 1 39 Erigonidae 5 4 2/ 0 0/ 0 1 12 Dictynidae 2 2 1/1 0/ 0 0 6 Linyphiidae 0 0 0/ 0 1/0 0 1 Thomisidae 0 0 0/ 0 1/0 0 1 Gnaphosidae 0 0 0/ 0 0/ 0 1 1 Unidentified 3 1 0/ 0 0/ 1 0 5 Orthoptera 0 0 2/0 3/ 6 10 21 Coleoptera 9 2 0/ 6 2/0 1 20 Lithobiomorpha 0 2 1/11 0/ 3 0 17 Collembola 0 2 0/ 1 0/ 1 2 6 Dermaptera 0 1 0/ 0 1/3 0 5 Lepidoptera 0 0 1/ 3 0/ 0 0 4 Hymenoptera 0 1 0/ 1 0/ 0 0 2 Total 20 80 32/92 28/55 24 331 February 1975 YEARGAN: SPIDER PREY IN ALFALFA 139 I. 2. oJ 80 .c •.• oJ 5. 6. (7l,- .cui 1200 g''- 200 6 5I cI ~~- -g,r- U U oI I o o U 5 °0 40 °0 o U z- 100 dO o z- 3 °0 600 CL.. CL.. z- z- C ••• C'" C'- CL.. ~Q. ~Q. g~ 0", ABCDEF A BC DE F ~ ~Q. Pordoso romu/oso CicodQ:llidoQ: June - Sept. N = 977 July - Sept. N·3037

4. Downloaded from https://academic.oup.com/ee/article/4/1/137/2395486 by guest on 27 September 2021 .g,~ 7. 8. .... 20 ~~ 300 .c . "':r g'I §'i 8 2 ~8 dO ~o z- 10 zQ 150 z-00 C,- CL.. 0 ••• C ••• c,- C'- ...Q. ~Q. g~ g~ ~ ~ ~ ABCDEF ABCDEF Geocoris spp. Col/insia p/umosa June - Aug. N=182 Sept. N=988 June - Aug. N=32 FIG. 5-8.-Mean numbers of arthropods caught in pit- A= 7am-12noon D= 6pm-12mdnt. fall traps during various periods of the 24-h day in al- B= 12noon - 5pm E= 12mdnt.- 4 am falfa fields, Yolo Co., Calif., 1973. Taxon is followed by C= 5pm-8pm F= 4am-7am the months represented and the total number caught dur- Pacific Standard Time ing these months. Time periods are the same as in Fig. 1-4. FIG. 1-4.-Mean numbers of arthropods caught in pit- fall traps during various periods of the 24-h day in al- falfa fields, Yolo Co., Calif., 1973. Taxon is followed Members of these taxa were also active during the by the months represented and the total number caught during these months. rest of the 24-h cycle, however, and were occasion- ally taken as prey by P. ramulosa (Table 1). The common base before graphing, i.e., the number caught per 100 h of trapping in each time period. 9. 10. The results presented are for the months of greatest oJ catch of the various taxa. Although slight changes ~E 4 .g,~- 4 in diel activity occurred as the season progressed, elI oI U U graphical analysis of monthly catches showed that o o dO dO the activity pattern remained relatively constant dur- z- 2 z- 2 CL.. ing the periods for which results are presented. The cC'-••• C"" time periods, which remained constant during the ~"'Q. ~Q. study, were initially chosen so that periods C and ABCDEF F always included sunset and sunrise, respectively Parasitic HymQ:noptQ:ra (Fig. 1-11). June - Oct. N-131 Only the spider Co/linsia plumosa (Emerton) con- formed (chi-square not significant at the 5% signifi- II. cance level) to a hypothetical 1: 1:1:1: 1: 1 ratio for .•.. 60 the 6 time periods. Pardosa ramulosa was strongly ~~ I diurnal with very little activity from 8 PM to 4 AM 8 .0 (Fig. 1). The predation observations presented in °0 30 Table 1 therefore represent feeding by P. ramulosa z- CL.. during its primary activity period. c"" The family Cicadellidae, which was represented ~Q. in the pitfall catches primarily by A. obscura, had ABCDEF a diurnal activity pattern (Fig. 2) similar to that of Pholongidoe P. ramulosa. Geocoris spp. (primarily G. atricolor) June - Oct. N = 1342 were even more diurnal (Fig. 3). Gryllids were quite FIG. 9-11.-Mean numbers of arthropods caught in active throughout the 24-h cycle, except for de- pitfall traps during various periods of the 24-h day in al- pressed activity during the dawn period (Fig. 4). falfa fields, Yolo Co., Calif., 1973. Taxon is followed by the months represented and the total number caught dur- Staphylinids, collembolans, and pea aphids all were ing these months. Time periods are the same as in Fig. most active during the dusk period (Fig. 5-7). 1-4. 140 ENVIRONMENTAL ENTOMOLOGY Vol. 4, no. 1 erigonid spiders, C. plumosa and Spirembolus phylax Lepidoptera comprised less than 2 % of the observed Chamberlin and Ivie, were represented in the catches prey, the highest population densities of Lepidoptera primarily by males. Since both sexes were about (7 larvae/ff) occurred in August, concurrently with equally represented in population samples, this indi- peak numbers of P. ramulosa. Population peaks of cates that males of these species were more active P. ramulosa and the Egyptian alfalfa weevil, H. than the females. Although C. plumosa showed no brunneipennis, are very asynchronous, suggesting statistically significant periodicity, S. phylax was that this predator probably has little regulatory nocturnal with peak activity occurring during the effect on populations of California's currently most evening (Fig. 8 and 9). The parasitic Hymenop- important alfalfa pest. tera trapped, which were mainly Chalcidoidea, were essentially diurnal (Fig. 10). Phalangids were mainly Discussion nocturnal in activity (Fig. 11), as Williams (1962) and others have found in various other habitats. Although P. ramulosa feeds on a wide variety of Downloaded from https://academic.oup.com/ee/article/4/1/137/2395486 by guest on 27 September 2021 taxa in alfalfa, it appears that most of Seasonal Abundance its prey belong to relatively few groups, particularly The seasonal population trends of P. ramulosa the Hemiptera, Diptera, and Araneae. These results and three representative prey taxa are shown in Fig. are similar to those obtained in other studies of the 12-15. The general population pattern of P. ramu- prey of wolf spiders. Edgar (1969) found that ca. losa is similar to those of leafhoppers (primarily A. 85 % of the observed prey of Lycosa lugubris (WaI- obscura) and Geocoris spp. Population estimates of ckenaer) in an oak woodland in Scotland was com- Diptera and Lepidoptera were so variable that reli- posed of Diptera, Hemiptera (primarily Auchenor- able seasonal patterns were not established. Although rhyncha), and Araneae. Hallander (1970) reported

Fig. 13 Fig. 12

N (\j ~ 1-: l.L. 600 u... o o C\J C\J '" 280 Ci z Z 300 z 40 z « « w w ~ :! J F M A M J J A SON 0 J J F M A M J J A SON 0 J MONTH MONTH

Fig. 15 Fig. 14

(\j (\j I-' ~ l.L. u.. 3000 150 0 o C\J C\J c; Ci 1500 Z 75 z z «Z « w w ~ ~ J F M A M J J A SON D J J F M A M J J A SON D J MONTH MONTH

FIG. 12.-Population trends of Pardosa rarnulosa in alfalfa fields, Yolo Co., Calif., 1973. FIG. 13.-Population trends of Cicadellidae in alfalfa fields, Yolo Co., Calif., 1973. FIG. 14.-Population trends of Geocoris spp. in alfalfa fields, Yolo Co., Calif., 1973. FIG. 15.-Population trends of Egyptian alfalfa weevil larvae in alfalfa fields, Yolo Co., Calif., 1972. February 1975 YEARGAN: SPIDER PREY IN ALFALFA 141 that Diptera and Araneae were the most frequently Of 65 observations of P. ramulosa feeding on taken prey of both P. pullata Clerck and P. chelata spiders, 39 were cases of cannibalism. Edgar (1969) O. F. Muller in various habitats in southern Sweden. and Kiritani et al. (1972) also noted that the species Kiritani et a!. (1972), in the most extensive field of wolf spiders that they studied fed more frequently study of the prey of wolf spiders reported to date, on members of their own species than on other found that Auchenorrhyncha constituted ca. 80% species of spiders. Although both adult and juvenile of the prey of Lycosa pseudoannulata (Boesenberg P. ramulosa were observed feeding on members of and Strand) in rice paddies in Japan. The results of their own species, immature spiders were the victims these studies conducted in various ecosystems in in all observed cases of cannibalism except one, when different parts of the world suggest that although an adult female fed on an adult male. This study wolf spiders are indeed general predators, certain did not attempt to analyze the mortality factors con-

prey taxa may be more important than others. In tributing to the population dynamics of P. ram IIlosa, Downloaded from https://academic.oup.com/ee/article/4/1/137/2395486 by guest on 27 September 2021 all 4 studies, including the present investigation, one but these observations suggest that canibalism may or more of the same 3 orders of arthropods were be a significant mortality factor. the most frequently observed prey. In laboratory and field observations I have noted Acknowledgment that P. ramulosa reacts more frequently to prey that I thank W. R. Cothran, A. A. Grigarick, and E. move suddenly than to those that move slowly. I. Schlinger for their helpful suggestions during this Rapid movements are characteristic of such impor- study and for critically reviewing the manuscript. tant prey taxa as leafhoppers and Diptera. If a prey I am also grateful to J. H. Benedict for his assistance species is to be successfully utilized by a predator during the study, particularly in the aspects dealing it must not only fulfill certain behavioral and mor- with Geocoris spp. phological criteria, but must also occur together with the predator in time and space. The relatively low REFERENCES CITED frequency of feeding by P. ramulosa on abundant Dietrick, E. J., E. I. Schlinger, and R. van den Bosch. species of lepidopterous larvae may be in part due 1959. A new method for sampling arthropods us- to their microhabitat separation from this ground- ing a suction collecting machine and modified Ber- dwelling predator. Prey species such as A. obscura, lese funnel. 1. Econ. Entomol. 52: 1085-91. G. atricolor, and species of Ephydridae are com- Dondale, C. D., J. H. Redner, and R. B. Semple. 1972. monly found on the ground in a]falfa fields. The Diel activity periodicities in meadow arthropods. Can. J. Zool. 50: 1155-63. similarities of seasonal abundance and die] activity Edgar, W. D. 1969. Prey and predators of the wolf patterns of A. obsclira and Geocoris spp. to those spider Lycosa lugubris. J. Zool. 159: 405-11. of P. ramulosa show that these species also fulfill Hallander, H. 1970. Prey, cannibalism, and micro- the temporal requirements of "good" prey species. habitat selection in the wolf spiders Pardosa c/relata Turnbull (1960) and others have observed that and P. pullata. Dikos 21: 337-40. seasonal changes in the prey taken by some spiders Kajak, A. 1965. An analysis of food relations be- appears to be related to changes in prey abundance. tween the spiders Aralleus comatus and A. quad- This appears to be true for P. ramulosa as exemp]i- ratus and their prey in meadows. Eko\. Pol. 13: fied by A. obscllra. This species, which was present 717-64. in low numbers in the late spring, was not observed Kiritani, K., S. Kawahara, T. Sasaba, and F. Nakasuji. as prey during Mayor June (Table 1). As the A. 1972. Quantitative evaluation of predation by spi- obscl~ra populations increased during the summer, ders on the green rice leafhopper, Nep/rotettix cillC- however, this species became an important item of ticeps, by a sight-count method. Res. Pop. Ecol. 13: prey. A similar trend was noted for Geocoris spp. 187-200. Both adult and immature spiders were observed Nicholls, C. F. 1970. Some entomologica] equipment. 2nd ed. Inform. Bull. Res. Inst. Belleville, 2. feeding on every order of prey taken except Lepidop- Turnbull, A. L. 1960. The prey of the spider Li- tera, which were only observed to be taken by Ilyphia triangularis. Can. J. ZooI. 38: 859-73. adults. It appears that adults and immatures feed Williams, G. 1958. Mechanical time-sorting of pitfall on the same taxa, although the stages and/or pro- captures. J. Anim. Ecol. 27: 27-35. portions taken may vary. Due to changes in the 1962. Seasonal and diurnal activity of harvestmen age structure and density of predator and prey and spiders in contrasted habitats. Ibid., 31: 23-42. populations during the study, it was difficult to Yeargan, K. V., and C. D. Doodale. 1974. The spider determine whether the prey of adults differed sub- fauna of alfalfa fields in northern California. Ann. stantially from that of the immatures. Entomol. Soc. Am. 67: 681-2.