Natural Enemies of Entomopathogenic Nematodes

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Abstract

Entomopathogenic nematodes and their symbiotic bacteria have their own guild of natural enemies, but quantitative data to document the long-term effects of these natural enemies on entomopathogenic nematode populations are scant. Because entomopathogenic nematodes occur in the soil, it is difficult to quantify the effects of these natural enemies in the soil habitat. However, even in non-soil situations, the natural enemies of the nematode/bacterium complex are not well known. Thus, the only documented pathogens of the symbiotic bacteria, Xenorhabdus and Photorhabdus, are phages that can cause lysogeny and reduce the developing nematodes' food supply or negatively affect the nematode/bacterium's efficacy. Protozoan natural enemies (i.e., three microsporidian species) infect steinernematid nematodes, and one species adversely affects the longevity of the infective juveniles. In the nematodes' more natural habitat, nematode-trapping fungi, such as Arthrobotrys oligospora, Monacrosporium eudermatum and Geniculifera paucispora, can reduce infective juvenile populations in pasteurized and raw soil. With the endoparasitic fungus, Hirsutella rhossiliensis, higher mortality of Steinernema glaseri occurred compared with Heterorhabditis bacteriophora. Differential susceptibility to the fungus may be associated with the retention of the second-stage cuticle by H. bacteriophora. Invertebrate predators including mites and collembolans feed on the infective juveniles of entomopathogenic nematodes. Scavengers, especially several ant species feeding on nematode-killed insects, can adversely affect the developing entomopathogenic nematodes. Ants readily feed on steinernematid-killed insects but tend to avoid heterorhabditid-killed insects. Photorhabdus bacteria associated with heterorhabditid nematodes appear to produce a deterrent factor that prevents the ants from feeding on the cadaver.

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