Assessing the impact of microbial pesticides on nontarget insects: Laboratory versus field tests

Many entomopathogenic fungi that are used as microbial pest control agents (MPCAs) have the potential to infect non-target, beneficial insects, such as insect predators and parasitoids. The susceptibility of a predatory beetle, Hippodamia convergens (Coleoptera: Coccinellidae), to five entomopathogenic fungi was tested using laboratory bioassays. These fungi, Metarhizium anisopliae, Paecilomyces fumosoroseus, Nomuraea rileyi, and two strains of Beauveria bassiana, are all being developed as MPCAs. Laboratory bioassays are sometimes used to determine the potential for non-target effects, but may not be good predictors of field effects. A case study was conducted here to compare laboratory and field evaluations of B. bassiana effects on H. convergens, and to assess the effects of various factors which may have caused the observed differences.; In bioassays, the entomogenous fungi M. anisopliae and an aphid derived strain of B. bassiana caused up to 97 and 95% mortality, respectively, in H. convergens. P. fumosoroseus and a beetle derived strain of B. bassiana were moderately pathogenic, causing 75% and 56% mortality, respectively. N. rileyi lacked pathogenicity. Field mortality of H. convergens after treatment with B. bassiana (the aphid derived strain) varied greatly within a single season, mortality being 75-95% early in the season, when it was cool and wet, but negligible during the drier, late season. In greenhouse trials, differences in fungal exposures in laboratory vs. spray treatments had no effect on mycosis levels, but environmental conditions did. In general, the results of field tests were too variable to evaluate the potential for an MPCA to pose risks.; In the laboratory, temperature and humidity influenced both fungal activity and insect susceptibility. Percent germination of conidia was not affected by temperatures between 15-30{dollar}spcirc{dollar}C, yet mycosis levels were reduced at temperatures above 20{dollar}spcirc{dollar}C. Also, infections occurred at humidities below that required for in vitro conidial germination, suggesting that the insect cuticle may provide some moisture, although increasing the period of exposure to 96% RH increased mycosis. Incorporating environmental variables into laboratory assays should prove useful for determining the kinds of environments in which a MPCA may be active, helping to improve predictions of field effects.