Biotic Factors

1. Timper-P; Kaya-HK. 1989. Role of the second-stage cuticle of entomogenous nematodes in preventing infection by nematophagous fungi. Journal-of-Invertebrate-Pathology. 1989, 54:3, 314-321.
AB:Third-stage infective juveniles (dauers) in the nematode genera Steinernema [Neoaplectana] and Heterorhabditis are ensheathed in their second-stage (J2) cuticles. Retention of the J2 cuticle by various species and strains of Neoaplectana and Heterorhabditis spp. (89-100%) retained their J2 cuticles whereas Neoaplectana spp. (100%) lost theirs. When dauers of Neoaplectana and Heterorhabditis spp. with and without J2 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 coniospora), those without a J2 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 J2 cuticle of Neoaplectana spp. In contrast, conidia of both fungi adhered to the J2 cuticle of Heterorhabditis spp. but <0.7% of the dauers were infected. These results suggest that Heterorhabditis spp. may be better biological control agents of insects than Neoaplectana spp. in soils where nematophagous fungi are significant mortality factors.

2. Epsky-ND; Walter-DE; Capinera-JL. 1988. Potential role of nematophagous microarthropods as biotic mortality factors of entomogenous nematodes (Rhabditida: Steinernematidae, Heterorhabditidae). Journal-of-Economic-Entomology, 81:3, 821-825; 31 ref.
AB: The potential for nematophagous mites and Collembola to reduce survival of entomogenous nematodes was tested in laboratory studies. The majority of the arthropods tested were observed feeding on Steinernema feltiae [Neoaplectana carpocapsae] (Breton strain) and Heterorhabditis heliothidis (NC strain) infective stage juveniles. Phoresy of infective N. carpocapsae on many of the mites was observed, with infectives forming rafts of tightly packed nematodes on the dorsum of some of the larger mites. Such infectives remained viable and could move off the mite to kill prepupae of Galleria mellonella. Only one species of mesostigmatid mite, Gamasellodes vermivorax, was able to complete development on infectives, and survival was poor. An endostigmatid mite, Alycus roseus, and a collembolan, Hypogastrura scotti, were able to complete development from late-instar nymph to adult and to produce viable eggs on N. carpocapsae. In laboratory studies, there was a negative correlation between G. vermivorax number and moth prepupal mortality, demonstrating loss in nematode efficacy caused by predation by the mesostigmatid mite. There was also a significant difference between LD50 estimates obtained when mites were present or absent. Thus, nematophagous microarthropods are a biotic factor that could limit survival of field-applied entomogenous nematodes.