Interactions of two natural enemies ofTetranychus urticae, the fungal entomopathogenBeauveria bassianaand the predatory mite,Phytoseiulus persimilis

The effect of either untreated or treated adults of the spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) by Beauveria bassiana (Bals.) Vuillemin (Ascomycota: Hypocreales) DEBI008 at 1×106 (conidia/ml) was investigated on developmental stages and life table parameters of Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) under laboratory conditions. Four time intervals (0, 24, 48 and 72 h post-inoculation of spider mites) were considered for studying the predator characteristics as different treatments. Duration of each life stage, longevity, reproduction rate, intrinsic rate of natural increase (r m ), net reproductive rate (R 0), mean generation time (T) and finite rate of increase (λ) of the P. persimilis were calculated on both untreated and B. bassiana treated spider mite adults. Data analysis showed that longevity and fecundity of predatory mites fed on untreated and treated mites (time interval 0) were higher in comparison with other time intervals after inoculation. The entomopathogenic fungus adversely affected longevity and fecundity of the predatory mite. Fertility life table parameters of predatory mites fed on T. urticae treated by B. bassiana at different time intervals showed that T, R 0, λ and r m are strongly affected by the fungus presence and these parameters had significant differences among time treatments. The least r m value was observed in the time interval of 72 h post-inoculation. The fitness of T. urticae was affected by B. bassiana 24, 48 and 72 h post-inoculation of mite adults, and consequently it caused decreased longevity of P. persimilis and accordingly a decrease in the intrinsic rate of natural increase of the predator.