Investigations into the development of cross-tolerance in the Diamondback Moth (Plutella xylostella L., Yponomeutidae: Lepidoptera) to the entomopathogenic fungus Beauveria bassiana (Bal.) Vuillemin (Deuteromycotina: Hyphomycetes) and the toxin Dipel of Bacillus thuringiensis

The present research represents the first investigations into the development of crosstolerance in the larvae of Diamondback Moth (DBM) tolerant to Bacillus thuringiensis toxin (Bt-toxin: Dipel) and treated with different concentrations of the entomopathogenic fungus Beauveria bassiana (strain BbGHA). Significant differences (at P = 0.05) were obtained between the fungus concentrations used for the treatment of Bt-tolerant and susceptible DBM larvae. The LC50 of the fungus concentrations used for the treatment of Bt-tolerant larvae was 7,700,836.787 (7.7 X 10) conidia/ml versus 133,791.018 (1.3 X 10) conidia/ml for the susceptible larvae. The calculated resistance ratio (RR) was 57.6 times more in the Bt-tolerant larvae compared to the susceptible larvae. Overall, results suggest that Bt-tolerant larval populations of DBM could be controlled by application of B. bassiana, but higher concentrations of the fungal agent than in susceptible larval populations are required. Department of Plant Production & Protection, Faculty of Agriculture, An-Najah National University, Nablus, West Bank, Palestine. Insect Molecular Biology Laboratory, Department of Applied and Molecular Ecology, School of Agriculture, Food & Wine, Adelaide University, Waite Campus, Glen Osmond, SA, 5064, Australia.Entomology Unit, South Australian Research & Development Institute (SARDI), Waite Campus, Glen Osmond, SA, 5064, Australia Investigations into the development of cross-tolerance in the Diamondback Moth (Plutella xylostella L., Yponomeutidae: Lepidoptera) to the entomopathogenic fungus Beauveria bassiana (Bal.) Vuillemin (Deuteromycotina: Hyphomycetes) and the toxin Dipel of Bacillus thuringiensis