Laboratory investigation on the virulence of two isolates of the entomopathogenic fungus Beauveria bassiana against the twospotted spider mite Tetranychus urticae (Acari: Tetranychidae).

The virulence of Beauveria bassiana to one of the most important pests of agricultural and ornamental plants, Tetranychus urticae, was assessed by inoculating mites with different isolates (DEBI008, EUT116) and different concentrations of conidia (1 × 104, 1 × 105, 1 × 106, 1 × 107, and 1 × 108 conidia/ml). Treated mites were kept in controlled conditions at 25 ± 1°C, 60-70% RH and a photoperiod of 16:8 h (L: D) and mite mortality was determined daily. Mortality was found to increase with time and was dependent on time and conidia concentration, with values ranging from 4.06% on day 3 at a concentration of 1 × 104 to 82.81% on day 7 at a concentration of 1 × 108 for the lowest and highest conidia concentrations of the EUT116 isolate and from 4.37 to 74.68% for the DEBI008 isolate, respectively. The calculated median lethal concentration on the sixth day was 3.7 × 105 conidia/ml for the EUT116 isolate and 2.9 × 106 conidia/ml for the DEBI008 isolate. The median lethal time for T. urticae with conidial treatments EUT116 and DEBI008 were 4.56 and 5.16.days, respectively. Our research showed that isolate EUT116 can be effective in controlling T. urticae and this isolate is a promising candidate for microbial control of twospotted spider mite. [ABSTRACT FROM AUTHOR]