The entomopathogenic fungus Beauveria bassiana and its compatibility with Phytoseiulus persimilis (Acari: Phytoseiidae): Effects on Tetranychus urticae (Acari: Tetranychidae)

Two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) is an economically important pest that devastates varieties of crops worldwide and develops significant resistance to common chemical pesticides. Ovicidal effects of two isolates of entomopathogenic fungus, Beauveria bassiana (Balsamo) Vuillemin (isolates F and J. B.) were evaluated on the eggs of T. urticae using a spray method at 25 ± 2°C, 60–70٪RH and a photoperiod of 16:8 h (L: D). Egg mortality was determined by using different concentrations of conidia (1 × 103, 1 × 104, 1 × 105, 1 × 106, 1 × 107, and 1 × 108 conidia/ml). Mortality was found to increase with time and was dependent on time and conidia concentration, ranging from 4. 06% on day 3 at a concentration of 1 × 103 to 84. 37% on day 7 at a concentration of 1 × 108 for the F isolate and from 1. 87 to 65% for the J. B. isolate, respectively. This study also investigated the direct spray of the entomopathogenic fungus, Beauveria bassiana (isolates F and J. B.) on the predatory mite, Phytoseiulus persimilis (Athias-Henriot) under laboratory conditions. The predator adults were susceptible to isolate F (total mortality ± SE: 35 ± 1. 97% on the seventh day) but least susceptible to isolate J. B. (total mortality ± SE: 27. 25 ± 1. 33% on the seventh day). Moreover, viability of P. persimilis after spraying fungal isolate of J. B. on bean leaf discs at three time intervals (0, 24 and 48 hours) showed no significant difference. Further knowledge is needed to adjust the timing of various releases of both biological control agents to obtain maximum effectiveness in the greenhouse with minimum impact of the fungus on the predator.