Effect of Spiders on Inoculated Populations of the Migrant Skipper

Appl. Entomol. Zool. 42 (1): 27–33 (2007) http://odokon.org/

Effect of spiders on inoculated populations of the migrant skipper Parnara guttata guttata Bremer et Grey (Lepidoptera: Hesperiidae) in untilled and tilled paddy ﬁelds

Takashi MOTOBAYASHI,1,* Chikara ISHIJIMA,2,† Mihoko MURAKAMI,1 Motonori TAKAGI,1 Ayame TAGUCHI,1 Kazumasa HIDAKA3 and Yasuhisa KUNIMI2 1 Field Science Center, Faculty of Agriculture, Tokyo University of Agriculture and Technology; Fuchu 183–8509, Japan 2 Department of Bioregulation and Biointeraction, Graduate School of Agriculture, Tokyo University of Agriculture and Technol- ogy; Fuchu 183–8509, Japan 3 University Farm, Faculty of Agriculture, Ehime University; Hojo 799–2424, Japan (Received 19 May 2006; Accepted 21 August 2006)

Abstract To examine the effects of spider predation on pest populations in untilled paddy fields, we constructed life tables for immature stages of the migrant skipper Parnara guttata guttata Bremer et Grey artificially inoculated into untilled and tilled paddies in 2000 and 2001, and conducted a spider removal experiment in 2001. The life tables showed that the migrant skipper larval mortality rate was significantly higher in untilled than in tilled paddies. Unknown factors mainly contributed to this high mortality rate in untilled paddies. The spider removal experiment suggested that the presence of spiders was related to the high mortality rate of migrant skippers in untilled paddies.

Key words: Life table; migrant skipper; no-tillage; paddy ﬁelds; spider assemblage

sect pests (Itô et al., 1962; Kiritani et al., 1972; INTRODUCTION Kiritani and Kakiya, 1975; Oraze and Grigarick, Generalist predators, including ground beetles 1989). Planthopper density tended to be lower in and spiders, occur in higher numbers in no- or untilled than in tilled paddies, and the spatial distri- reduced-tillage than in conventional-tillage upland bution of wolf spiders overlapped that of planthop- cropping systems (House and All, 1981; Blumberg pers (Ishijima et al., 2004). Enhancement of the and Crossley, 1983; House and Parmelee, 1985; spider assemblage by no-tillage management prac- Robertson et al., 1994). Furthermore, the full gen- tices may reduce other rice insect pests. Parnara eralist predator assemblage that occurs with no- guttata guttata Bremer et Grey (migrant skipper) is tillage management has reduced pest populations one of the major pests in paddy fields in central and plant damage in upland crops (Brust et al., and western Japan. In our study fields, migrant 1985; Clark et al., 1994). skippers were observed every year; thus, we ana- Hidaka (1993, 1997) showed that Lycosidae lyzed the life tables of immature populations of mi- (wolf spiders) were more abundant in winter mulch grant skippers in untilled and tilled paddy fields. and untilled paddy fields than in conventionally tilled paddy fields. Previous studies have also MATERIALS AND METHODS shown that the spider assemblage, including wolf spiders, was enhanced by no-tillage management in Study fields. The study was conducted in rice paddy fields (Ishijima et al., 2004; Motobayashi et paddies of the Tokyo University of Agriculture and al., 2006). Spiders have been characterized as the Technology on Fuchu campus, Tokyo, Japan, dur- most important biological control agent of rice in- ing the growing seasons of 2000 and 2001. In

*To whom correspondence should be addressed at: E-mail: [email protected] † Present address: Laboratory of Entomology, Department of Tea, National Institute of Vegetable and Tea Science, Kanaya, Shizuoka 428–8501, Japan DOI: 10.1303/aez.2007.27

27 28 T. MOTOBAYASHI et al.

2000, we used two paddy fields divided into 12 370-m2 plots. In 2001, we used one paddy field divided into six 370-m2 plots. These plots were sys- tematically assigned to one of two tillage treatments: untilled or tilled (Fig. 1). All fields were ir- rigated in early May, and 20-day-old rice (Oriza sativa L., variety Tukinohikari) seedlings were transplanted into the field in mid-May at a density of 16.7 hills m2. Plastic flashing (25 cm in height) was placed on the sides of each plot to prevent spider emigration and immigration. No insecticides or fungicides were applied during the experimental period. The cultivation procedure is described in Motobayashi et al. (2006) in detail. Life tables of the migrant skipper. To evaluate the effect of spider assemblage on insect pests in untilled and tilled paddy fields, we used life-table analysis for an artificially inoculated larval population of the migrant skipper. In central and western Fig. 1. Arrangement of experimental plots in 2000 and Japan, the skipper has three discontinuous genera- 2001. NT indicates untilled plots; T indicates tilled plots. tions per year (Ishii and Hidaka, 1979). Adults of the overwintering generation emerge in late May. These adults produce a low-density first genera- and the fifth-instar larvae pupated in the nest. The tion, whose adults emerge in early to mid-July. nest was remade at every molt. These habits make These adults produce the second generation in the it easy to estimate the number of insects in each middle of the rice season, and the density of the developmental stage (Nakasuji, 1982). All larvae second generation is considerably higher than that and pupae were counted, and nests were marked of the first generation. Adults of the second genera- using a felt-tipped pen at intervals of 2–3 days until tion emerge in late August to mid-September and adults emerged. migrate en masse. The most damage to rice plants Mortality factors were estimated as follows. Un- by this species occurs during the second genera- hatched eggs were collected and reared in the labo- tion. Yoshizawa (1996) estimated that a 10% yield ratory to obtain egg parasitoids. After egg para- loss of rice was caused by larvae of the second sitoids emerged, the remaining unhatched eggs generation at a density of one insect per hill. were dissected to estimate egg mortality caused by Although skippers occurred every year in the parasitism or physiological factors. First-instar lar- study fields, their density was too low to construct vae that were missing on the first census date after life tables in 2000 and 2001. Thus, skipper eggs hatching were regarded as having died from a fail- were artificially inoculated onto rice plants follow- ure to settle on leaves. Parasitoid pupae and co- ing the methods of Matsumura (1992). Four cages coons discovered during the census were brought (1.8 m1.8 m1.5 m) with 2-mm mesh netting, to the laboratory and reared until adults emerged. which covered 40 hills, were set up on untilled and Mortality caused by physiological death was esti- tilled plots (Fig. 1). Ten pairs of mature skipper mated as the percentage of brownish shrunken lar- adults reared in the laboratory at 25°C and 16L: 8D val corpses. were introduced into each cage on 1 August 2000 Spider removal experiment. To estimate mor- and 10 August 2001. These adults were allowed to tality caused by spider predation, we conducted a lay eggs for 1 day. The adults were then caught and spider removal experiment in mid-August 2001 the cage was removed. All eggs were counted 2 (Fig. 1). We constructed six enclosures (spider re- days after introduction. Leaves with eggs were moval subplot) of plastic plates measuring 75 cm marked using a felt-tipped pen. After hatching, 60 cm25 cm (lengthwidthheight) smeared each larva constructed a nest of folded rice leaves, with tanglefoot (Fujiyakuhin Industrial Co., Ltd., Effect of Spider Predation in Untilled Paddies 29

Tokyo, Japan). Each enclosure contained ten rice rate due to unknown factors was higher in the un- hills. All spiders were removed from the spider tilled than tilled treatment (Tables 1 and 2). As a removal subplots by hand or by using suction result, the survival curves were similar between apparatus. Spiders were also removed by hand two tillage treatments at early larval stages; however, or three times during the study period. Fourth-in- survival decreased rapidly in untilled plots com- star larvae of the migrant skipper reared in the lab- pared to tilled plots at later larval stages (Fig. 2). oratory were inoculated at a density of three indi- Spider predation was thought to be the main viduals per hill. Rice plants bordering the plots cause of unknown mortality because the only effec- were cut to prevent the immigration of spiders and tive predators we observed in the study fields were emigration of inoculated larvae. Likewise, fourth- spiders; however, we had no direct evidence and instar larvae were inoculated on ten rice hills in thus conducted the spider removal experiment. each unmanipulated subplot, and the neighboring Two-way ANOVA showed significant effects of plants were cut. We counted larval survival in each spider removal (F72.96, p0.001) and tillage plot one week after inoculation. treatment (F11.31, p0.01) on the mortality of Data analysis. For life tables, the survival at fourth instar larvae (Fig. 3), but the correlation be- each developmental stage or by each mortality fac- tween spider removal and tillage treatment was not tor was tested using Chi-square tests. significant (F3.91, p0.05). Dead larvae were For the spider removal experiment, mortality rate rarely found on rice plants, and we did not observe data were arcsine-square-root-transformed prior to any predators other than spiders in the experimen- analysis and analyzed using two-way ANOVA. tal plots.

RESULTS DISCUSSION Life tables for the immature stage of migrant Parasitism was the most important cause of egg skippers artificially inoculated in each treatment in and larval mortality in the life table of the migrant 2000 and 2001, and the survival curves of these in- skipper. These parasitoid species have been re- oculated populations are shown in Tables 1 and 2, ported as the primary parasitoids of the migrant and Fig. 2, respectively. skipper, but the diversity of parasitoid species was Egg parasitoids were the most important mortal- lower than that observed in previous studies (Naka- ity factor in the egg stage. Two egg parasitoids, Te- suji, 1982; Matsumura, 1992). However, there was lenomus sp. and Trichogramma sp., were found in no significant difference in mortality caused by both years. Parasitoids were also a major source of parasitism in untilled and tilled paddy plots. Mor- mortality during late larval to pupal stages. Apan- tality caused by unknown factors was also impor- teles baoris Wilkinson emerged from fourth and tant at late larval stages, and was significantly fifth instar larvae, whereas Pediobius mitsukurii higher in untilled than in tilled paddies. Previous (Ashmead) and Thecocarcelia thrix Townsend studies have indicated that spider abundance and were observed at the pupal stage. Although the per- biomass was significantly greater in untilled than in centage of parasitism was high, no difference was tilled paddies in late August to early September observed between treatments in the mortality rate (Ishijima et al., 2004; Motobayashi et al., 2006). caused by parasitism (egg stage: c 20.18, p0.05 Polistes wasps (Nakasuji, 1982) and birds (Matsu- in 2000 and c 20.18, p0.05 in 2001; larval to mura, 1992) were reported as predators of late pupal stage: c 21.24, p0.05 in 2000 and c 2 larval-stage migrant skippers; however, these and 0.65, p0.05 in 2001). other predators were not observed in the experi- Unknown mortality factors were also important, mental fields. In our removal experiment, we could particularly in fourth and fifth instar larvae. We not count the number of spiders in the experimen- found significant effects of tillage treatment on the tal plots, whereas we did not observe any spiders in mortality rate of fourth and fifth instar larvae in the removal plots, although we observed some spi- 2000 (c 222.34, p0.01 and c 28.91, p0.01, ders in control (unmanipulated) plots. Thus, the respectively) and fifth instar larvae in 2001 (c 2 spider removal experiment suggested significant 8.78, p0.01). In these larval stages, the mortality predation by spiders on skipper larvae. These 30 T. MOTOBAYASHI et al.

Table1.Life tables of P. guttata guttata in untilled and tilled plots in 2000

Untilled plot Tilled plot

Developmental Mortality factor No. surviving No. dying % of No. surviving No. dying % of stage (x) (dxF) at start of within stage mortality at start of within stage mortality stage interval interval rate stage interval interval rate (lx) (dx) (100 qx) (lx) (dx) (100 qx)

Egg 1,130 1,520 Parasitoids 210 18.6 270 17.8 Unknown 70 6.2 70 4.6

280 24.8 340 22.4 Instar I 850 1,180 Failure in settlement 223 26.2 372 31.5 Physiological death 15 1.8 40 3.4

238 28.0 412 34.9 Instar II 612 768 Physiological death 0 0.0 0 0.0 Unknown 17 2.8 48 6.3

17 2.8 48 6.3 Instar III 595 720 Parasitoids 20 3.4 0 0.0 Physiological death 35 5.9 20 2.8 Unknown 35 5.9 70 9.7

90 15.1 90 12.5 Instar IV 505 630 Parasitoids 50 9.9 70 11.1 Physiological death 5 1.0 0 0.0 Unknown 250 49.5 170 27.0

305 60.4 240 38.1 Instar V 200 390 Parasitoids 70 35.0 110 28.2 Physiological death 0 0.0 10 2.6 Unknown 105 52.5 160 41.0

175 87.5 280 71.8 Pupa 25 120 Parasitoids 20 80.0 80 66.7 Physiological death 5 20.0 0 0.0

25 100.0 80 66.7 Adult 0 40 Accumulated mortality 100.0 97.4

Numbers are per 100 hills. Effect of Spider Predation in Untilled Paddies 31

Table2.Life tables of P. guttata guttata in untilled and tilled plots in 2001

Untilled plot Tilled plot

Egg 1,098.1 704.2 Parasitoids 399.6 36.4 245.9 34.9 Unknown 172.9 15.7 193.1 27.4

572.5 52.1 439.0 62.3 Instar I 525.6 265.3 Failure in settlement 208.0 39.6 68.1 25.7 Physiological death 53.8 10.2 59.8 22.5

261.8 49.8 127.9 48.2

Instar II 263.9 137.5 Physiological death 3.0 1.1 9.7 0.7 Unknown 24.8 9.4 29.2 21.2

27.8 10.5 38.9 21.9

Instar III 236.2 98.6 Parasitoids 6.5 2.8 0.0 0.0 Physiological death 6.5 2.8 0.0 0.0 Unknown 3.6 1.5 12.5 12.7

16.6 7.0 12.5 12.7 Instar IV 219.5 86.1 Parasitoids 48.6 22.1 23.6 27.4 Physiological death 3.6 1.6 2.8 3.3 Unknown 125.0 56.9 41.7 48.4

177.2 80.6 68.1 79.0 Instar V 42.5 18.1 Parasitoids 27.8 65.4 9.7 53.7 Physiological death 0.0 0.0 0.0 0.0 Unknown 14.7 34.6 0.0 0.0

42.5 100.0 9.7 53.7 Pupa 0.0 8.4 Parasitoids 0.0 0.0 4.2 49.7 Physiological death 0.0 0.0 0.0 0.0

0.0 0.0 4.2 49.7 Adult 0.0 4.2 Accumulated mortality 100.0 99.4

Numbers are per 100 hills. 32 T. MOTOBAYASHI et al.

Fig. 2. Survival curves of larvae inoculated artificially on rice hills in no-tilled and tilled plots. Closed symbols indicate untilled plots; open symbols indicate tilled plots. I–V, first to fifth instar larvae; P, pupa; A, adult.

late-stage larvae may be more susceptible to spider predation because of increased encounter fre- quency. Lycosid and salticid spider populations were enhanced by no-tillage management in the experimental fields. During late August to early Septem- ber, the abundance of lycosid and salticid spiders in untilled plots was 2–2.5-fold and 4–10-fold larger than tilled plots, respectively (Motobayashi et al., 2006). These spiders may mainly cause a re- duction in the late-stage larval skipper population; however, we could not clarify the contribution of each spider species to the predation of migrant skipper larvae. Further investigation is needed to evaluate the effects of spider assemblage on mi- Fig. 3. Mortality rate of inoculated 4th instar larvae as a grant skippers in untilled paddy fields. function of spider removal and tillage treatment. ACKNOWLEDGEMENTS results suggest that the spider assemblage reduced We thank Dr. F. Nakasuji of Okayama University for valu- the population of late-stage larval skippers, and to able advice regarding the life table study. We also thank Dr. M. a greater extent in untilled than in tilled paddies. Matsumura of the National Agricultural Research Center for The larval behavior of the migrant skipper may Kyushu Okinawa Region for identifying the skipper’s natural contribute to limit the effect of spider predation. enemies. We are also grateful to Mr. E. Yoshizawa of Nagano Prefecture Agricultural Research Center for providing the Larvae of this species construct a nest of rice skipper stock culture. leaves at each molt. We observed that early stage larvae construct their nests near their hatching po- REFERENCES sition, which is near the middle or lower layer of Blumberg, A. Y. and D. A. Crossley Jr. (1983) Comparison rice, and rarely wander around the nest. In contrast, of soil surface arthropod populations in conventional late-stage larvae construct their nests in the upper tillage and old field systems. Agro-Ecosystems 8: 247– layer of rice on the same or adjacent hill, and fre- 253. Brust, G. E., B. R. Stinner and D. A. McCartney (1985) quently wander around the nest to feed on rice Tillage and soil insecticide effects on predator-black leaves or make a new nest during the night (Mu- cutworm (Lepidoptera: Noctuidae) interactions in corn rakami et al., unpublished data). Consequently, agroecosystems. J. Econ. Entomol. 78: 1389–1392. Effect of Spider Predation in Untilled Paddies 33

Clark, M. S., J. M. Luna, N. D. Stone and R. R. Youngman tor-prey system in the paddy field. Res. Popul. Ecol. 17: (1994) Generalist predator consumption of armyworm 29–38. (Lepidoptera: Noctuidae) and effect of predator removal Kiritani, K., S. Kawahara, T. Sasaba and F. Nakasuji (1972) on damage in no-till corn. Environ. Entomol. 23: 617– Quantitative evaluation of predation by spiders on the 622. green rice leafhopper, Nephotettix cincticeps Uhler, by a Hidaka, K. (1993) Farming systems for rice cultivation sight-count method. Res. Popul. Ecol. 13: 187–200. which promote the regulation of pest populations by natu- Matsumura, M. (1992) Life tables of the migrant skipper, ral enemies: planthopper management in traditional, in- Parnara guttata guttata Bremer et Grey (Lepidoptera: tensive farming and LISA rice cultivation in Japan. Hesperiidae), in the northern peripheral area of its distri- FFTC Extension Bull. 374: 1–15. bution. Appl. Entomol. Zool. 27: 331–340. Hidaka, K. (1997) Community structure and regulatory Motobayashi, T., C. Ishijima, M. Takagi, M. Murakami, K. Hi- mechanism of pest populations in rice paddies cultivated daka and Y. Kunimi (2006) Effects of tillage practices under intensive, traditional organic and lower input or- on spider assemblage in rice paddy fields. Appl. Ento- ganic farming in Japan. Biol. Agric. Hortic. 15: 35–49. mol. Zool. 41: 369–379. House, G. J. and J. N. All (1981) Carabid beetles in soybean Nakasuji, F. (1982) Population dynamics of a migrant skip- agroecosystems. Environ. Entomol. 10: 194–196. per butterfly Parnara guttata (Lepidoptera: Hesperiidae): House, G. J. and R. W. Parmelee (1985) Comparison of soil survival rates of immature stages in paddy fields. Res. arthropods and earthworms from conventional and no- Popul. Ecol. 24: 157–173. tillage agroecosystems. Soil Tillage Res. 5: 351–360. Oraze, M. J. and A. A. Grigarick (1989) Biological control Ishii, M. and T. Hidaka (1979) Seasonal polymorphism of of aster leafhopper (Homoptera: Cicadellidae) and the adult rice-plant skipper, Parnara guttata guttata, and midges (Diptera: Chironomidae) by Pardosa ramlosa its control. Appl. Entomol. Zool. 14: 173–184. (Araneae: Lycosidae) in California rice fields. J. Econ. Ishijima, C., T. Motobayashi, M. Nakai and Y. Kunimi (2004) Entomol. 82: 745–749. Impacts of tillage practices on hoppers and predatory Robertson, L. N., B. A. Kettle and G. B. Simpson (1994) wolf spiders (Araneae: Lycosidae) in rice paddies. Appl. The influence of tillage practices on soil macrofauna Entomol. Zool. 39: 155–162. in northeastern Australia. Agric. Ecosyst. Environ. 48: Itô, Y., K. Miyashita and K. Sekiguchi (1962) Studies on the 149–156. predators of rice crop insect pests using the insecticidal Yoshizawa, E. (1996) The loss analysis and control threshold check method. Jpn. J. Ecol. 12: 1–12. of rice skippers, Parnara guttata. Plant Prot. 50: 18–20 Kiritani, K. and N. Kakiya (1975) An analysis of the preda- (in Japanese).