JOURNAL OF INVERTEBRATE PATHOLOGY 54, 314-321 (1989) Role of the Second-Stage Cuticle of Entomogenous Nematodes in Preventing Infection by Nematophagous Fungi PATRICIA TIMPER AND HARRY K. KAYA Department of Nematology, University of California, Davis, California 95616 Received October 24, 1988; accepted February 17, 1989 Third-stage infective juveniles (dauers) in the nematode genera Steinernema and Heterorhabditis are ensheathed in their second-stage (52) cuticles. Retention of the 32 cuticle by various species and strains of Steinernema and Heterorhabditis was determined after the dauers moved through 5 cm of sand. In general, Heterorhabditis spp. (89-100%) retained their 52 cuticles whereas Steinernema spp. (100%) lost theirs. When dauers of Steinernema and Heterorhabditis spp. with and without 52 cuticles (cuticles removed with either 0.05% sodium hypochlorite or passage through sand) were exposed to conidia of endoparasitic fungi (either Hirsutella rhossiliensis or Drechmeria conio- spora), those without a 52 cuticle and with conidia adhering to the J3 cuticle became infected by the fungi. Conidia of H. rhossiliensis and D. coniospora did not adhere to the 52 cuticle of Steinernema spp. In contrast, conidia of both fungi adhered to the 52 cuticle of Heterorhabditis spp. but 10.7% of the dauers were infected. These results suggest that Heterorhabditis spp. may be better biolog- ical control agents of insects than Steinernema spp. in soils where nematophagous fungi are sig- nificant mortality factors. Q 1989 Academic Press, Inc. KEY WORDS: Drechmeria coniospora; Heterorhabditis spp.; Hirsute/la rhossiliensis; Stei- nernema spp.; biological control; nematophagous fungi; second-stage cuticle. INTRODUCTION Entomogenous nematodes in the genera Steinernema and Heterorhabditis occur naturally in soil and show considerable po- tential as biological control agents of soil- dwelling insects (Kaya, 1985). Desirable characteristics of these nematodes are their high virulence, broad host range, ease of mass production, and ability to seek out hosts. The third-stage juvenile (dauer) is the infective as well as the environmentally resistant stage. The dauer is the only stage found outside the host and its body is en- sheathed in the second-stage cuticle (Poinar and Leutenegger , 1968). Steinernema and Heterorhabditis spp. require moisture to survive and infect a host; they are unable to survive above ground on exposed surfaces because of rapid desiccation (Kaya and Reardon, 1982). Soil retains a high relative humidity even at low water potentials (Simons and Poinar, 1973) and offers protection against solar radiation and temperature extremes. Therefore, it is considered the most suit- able environment for biological control of insects by Steinernema and Heterorhabdi- tis spp. (Gaugler, 1981). However, soil con- tains organisms that may antagonize ento- mogenous nematodes and limit their use as biological control agents of insects. The ob- servation that S. feltiae and S. glaseri dau- ers declined faster in nonsterilized soil than in sterilized soil (Ishibashi and Kondo, 1986) suggests that soil organisms can re- duce nematode persistence. Poinar and Jansson (1986a) reported that the conidia of Drechmeria coniospora ad- hered to and infected the developing stages of S. Ji?ltiae and Rhabditis sp., but rarely adhered to and never infected dauers of S. feltiae, S. bibionis, S. glaseri, S. interme- dia, and H. heliothidis. On the other hand, these same nematode species were suscep- tible to infection by the trapping fungi Mo- nacrosporium ellipsosporum and Arthro- botrys oligospora. Dauers trapped by M. ellipsosporum sometimes escaped infection by slipping out of their 52 cuticle (Poinar and Jansson, 1986b), though no mention was made of the proportion of escaping dauers or the importance of the 52 cuticle. 314 0022-201 l/89 $1.50 Copyright Q 1989 by Academic Press. Inc. All rights of reproduction m any form reserved.