Insecticidal efficacy of two isolates ofBeauveria bassiana(Bals.) (Vuill.), on the second larval stage ofLeptinotarsa decemlineata(Say) (Col.: Chrysomelidae)

Leptinotarsa decemlineata is a serious potato pest throughout the world that has developed resistance to many insecticides. This study investigated the virulence of two indigenous isolates of Beauveria bassiana, consisting of DEBI007 and IR1217C. Five different concentrations of each isolate, 1 × 107, 3.1 × 107, 1 × 108, 3.1 × 108 and 1 × 109 conidia ml−1, were applied in bioassay using dipping method on second instar larvae. Control insects were treated with distilled water containing 0.01% Tween-80 (Sigma, Germany) as surfactant. The results showed that mortality percentages due to DEBI007 and IR1217C isolates in the highest concentration were 60% and 57.77%, respectively. There was a significant difference between efficacies of different conidial concentrations; therefore, with rise in conidial concentration, the mortality percentage was increased. The DEBI007 isolate that was previously isolated from the soil was more effective than IR1217C isolate. Calculated LC50 for this effective isolate was 1.4 × 107 conidia ml−1, which, respectively, is the highest concentration.