Abstract
Entomopathogenic nematodes are typically considered lethal parasites of insect hosts. Indeed they are employed as such for biological control of insect pests. The effects of exposure to entomopathogenic nematodes are not strictly limited to mortality, however. Here we explore non-lethal effects of exposure to entomopathogenic nematodes by introducing the relatively non-susceptible pupal stage of Delia antiqua to thirteen different strains. We specifically chose to inoculate the pupal stage because it tends to be more resistant to infection, yet resides in the soil where it could come into contact with EPN biological control agents. We find that there is no significant mortality at the pupal stage, but that there are a host of strain-dependent non-lethal effects during and after the transition to adulthood including altered developmental times and changes in risk of death compared to controls. We also find that exposure to specific strains can reduce risk of mortality. These results emphasize the strain-dependent nature of entomopathogenic nematode infection and highlight the positive and negative ramifications for non-lethal effects for biological control of insect pests. Our work emphasizes the need for strain-specific screening of biological control agents before wide-spread adoption.
Highlights
Entomopathogenic nematodes are typically considered lethal parasites of insect hosts
Inoculating pupae with a spectrum of entomopathogenic nematodes strains had differential effects on survival, time spent as a pupae, and likelihood of mortality as an adult
Survival curves for D. antiqua inoculated with H. indica LW, S. carpocapsae, and S. glaseri NC were similar with non-inoculated controls
Summary
Entomopathogenic nematodes are typically considered lethal parasites of insect hosts. We find that exposure to specific strains can reduce risk of mortality These results emphasize the strain-dependent nature of entomopathogenic nematode infection and highlight the positive and negative ramifications for non-lethal effects for biological control of insect pests. While there have been notable successes in controlling insect pests through applications of entomopathogenic nematodes, it seems likely that non-lethal or sub-lethal effects of EPN infection could potentially have long-lasting impacts on insect hosts. In each of these cases, EPNs had distinct consequences for the life history of their host insects; discoloration, deformation, and delayed metamorphosis presumably will negatively impact the ability of these insects to reproduce
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