The selective toxicity efficacy of entomopathogenic Beauveria bassiana (Balsamo) fungus was evaluated against the
two spotted spider mite Tetranychus urticae Koch and its predator Stethorus gilvifrons (Muls) under laboratory condition.
The tested B. bassiana strain had been brought from Plant Protection Institute, Agricultural Research Center, Jokioinen,
Finland. The activation of B. bassiana was carried out using Tenebrio molitor (L.) larvae as a bait insect. Conidia of growing fungus were extracted and counting of spores was computed. Five concentrations of the conidial suspension were prepared (3.92 x104, 3.92 x105, 3.92 x106, 3.92 x107 and 3.92 x108 spores/ml). Results revealed that the mortality rates for both adult females of the mite T. urticae and the predator S. gilvifrons infected by B. bassiana were positively correlated with stranded stage concentration and time dependent. There was a latent eight-day period between infestation and mortality achievement in both tested organisms. On the eighth day, LC50 values of B. bassiana were 2.702 x105 and 2.208 x1012 spores/ml for adult females of T. urticae and 2nd instar larval stage of S. gilvifrons, respectively. Such selective toxicity was also noted at LC90 level where the values were 6.1987 x1010 and 2.839 x1017 for adult females of T. urticae and 2nd instar larvae of S. gilvifrons respectively. These results showed that the entomopathogenic fungus B. bassiana has a potent selective toxicity against adult females of T. urticae compared with second instar larvae of S. gilvifrons.