Laboratory evaluation of the effect of Beauveria bassiana on the predatory mite Phytoseiulus persimilis (Acari: Phytoseiidae)

- Sub-lethal effects of B. bassiana were assessed on eggs and adults of P. persimilis.
- B. bassiana spray on eggs has no effect on development, longevity, and sex ratio.
- B. bassiana spray on eggs affects life table parameters by reducing fecundity.
- B. bassiana affected negatively more on reproduction when sprayed in adult stage.
- P. persimilis was compatible when released after spraying B. bassiana.

Tetranychus urticae Koch (Acari: Tetranychidae), a major pest of many agricultural crops, is mainly controlled with chemical acaricides. However, predatory mites and entomopathogens have been proposed as alternative control agents. In this study, the effect of the BotaniGard® GHA strain of Beauveria bassiana on the survival, longevity, fecundity, and egg hatch rate of the predatory mite Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) were studied under laboratory conditions. When B. bassiana was applied directly to P. persimilis eggs at a concentration of 1 × 108 conidia/ml, corrected hatchability was less than 5%, and the corrected mortality of nymphs and adults was not significantly different from control 10 days after treatment. Phytoseiulus persimilis nymphs that hatched from treated eggs showed no significant change in their development time, adult female longevity, hatch rate, survival rates over time, or offspring sex ratio. However, significant negative effects on fecundity and life table parameters (net reproductive rate, intrinsic rate of natural increase, mean generation time, finite rate of increase, and doubling time) were found when B. bassiana was applied to the adult stage. Spraying B. bassiana at 1 × 108 conidia/ml on newly emerged adults of P. persimilis caused 44% reduction in the oviposition period, 26% in adult longevity, and 63% in fecundity. Due to these negative effects, B. bassiana should be used with careful adjustment of application timing (first spray B. bassiana and then release P. persimilis) to supplement biological mite control systems using P. persimilis.

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