Isolation, Characterization, and Formulation of Indigenous Beauveria bassiana Fungus Against Colorado Potato Beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

Abstract

In this study, a total of 12 different fungal isolates were obtained from two different Colorado potato beetle (CPB) populations to identify a new effective agent to control L. decemlineata, which has developed resistance to many chemicals. The isolates were defined as Beauveria bassiana based on the ITS1-5.8S-ITS2, EF1-α, RPB1, and Bloc gene sequences. Under laboratory conditions, all isolates were pathogenic, but their virulence was different on larvae and adults. LdA-1 was the most virulent isolate with a mortality of 80% in larvae and 50% in adults. The LC50 value of this isolate was determined to be 0.2×106 and 0.17×108 conidia/ml for larvae and adults, respectively. Based on these results, LdA-1 isolates were used for mycoinsecticide development. Conidia were produced by solid-state fermentation using rice as a substrate. The conidia were formulated as oil-in-water emulsions and their efficacy was evaluated. The efficacy of the oil-based formulation against CPB larvae and adults was tested on eggplant in pot experiments. The new oil-based product caused 100% and 97% mortality on larvae and adults, respectively, at 1×108 conidia/ml. The LC50 value of our formulation for larvae and adults was calculated to be 1.2×106 and 0.2×107 conidia/ml, respectively. These results highlight that this formulation could be a suitable product for CPB control instead of conventional synthetic insecticides.

Graphical Abstract

Abstract
In this study, a total of 12 different fungal isolates were obtained from two different Colorado potato beetle (CPB) populations to identify a new effective agent to control L. decemlineata, which has developed resistance to many chemicals. The isolates were defined as Beauveria bassiana based on the ITS1-5.8S-ITS2, EF1-α, RPB1, and Bloc gene sequences. Under laboratory conditions, all isolates were pathogenic, but their virulence was different on larvae and adults. LdA-1 was the most virulent isolate with a mortality of 80% in larvae and 50% in adults. The LC50 value of this isolate was determined to be 0.2×106 and 0.17×108 conidia/ml for larvae and adults, respectively. Based on these results, LdA-1 isolates were used for mycoinsecticide development. Conidia were produced by solid-state fermentation using rice as a substrate. The conidia were formulated as oil-in-water emulsions and their efficacy was evaluated. The efficacy of the oil-based formulation against CPB larvae and adults was tested on eggplant in pot experiments. The new oil-based product caused 100% and 97% mortality on larvae and adults, respectively, at 1×108 conidia/ml. The LC50 value of our formulation for larvae and adults was calculated to be 1.2×106 and 0.2×107 conidia/ml, respectively. These results highlight that this formulation could be a suitable product for CPB control instead of conventional synthetic insecticides.

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