Feeding on Beauveria bassiana-treated Frankliniella occidentalis causes negative effects on the predatory mite Stratiolaelaps scimitus.

The soil-inhabiting predatory mite Stratiolaelaps scimitus (Womersley) (Acari: Laelapidae) and the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Cordycipitaceae) can both serve as effective biocontrol agents against the pest Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). Assuming the fungus B. bassiana does not adversely affect S. scimitus, the combined application of these 2 agents could enhance the suppression of F. occidentalis. The age-stage, 2-sex life table was used in the present study to evaluate the effects of B. bassiana strain GZGY-1-3 on S. scimitus, mediated through F. occidentalis feeding. When S. scimitus fed on the prepupae of F. occidentalis that had been exposed to the GZGY-1-3 suspension for 24 h, the developmental times of protonymph, deutonymph, and preadult mites were significantly longer and the mites' longevity and fecundity were significantly lower than mites fed on untreated F. occidentalis. The intrinsic rate of increase (r), finite rate of increase (λ) and net reproduction rate (R0) of the mite population were all significantly lower in the treatment where B. bassiana was applied compared to untreated populations. Specifically, the indirect effects of B. bassiana on S. scimitus was mediated through mite consumption of fungus-infected pupae of F. occidentalis. Our results showed that the combined application of B. bassiana and S. scimitus may pose potential risks for the simultaneous biocontrol of F. occidentalis.