Esterase-mediated tolerance to a formulation of the organophosphate insecticide monocrotophos in the entomopathogenic fungus, Beauveria bassiana (Balsamo) Vuill: a promising biopesticide.

The use of biopesticides compatible with chemical pesticides is recommended in pest management as an effective and ecologically sound strategy. The entomopathogenic fungus Beauveria bassiana (Balsamo) Vuill, which is used as a biopesticide, was found to exhibit and lose tolerance to two organophosphorus insecticides widely used in Indian fields. The pattern of response is similar to the esterase-mediated organophosphate tolerance in aphids achieved through esterase gene duplication. Therefore the role of esterase in the tolerance exhibited by isolates of B. bassiana to the organophosphate, monocrotophos, was studied. Both the total soluble protein content and esterase activity were found to increase significantly in B. bassiana cultures that were able to grow in the presence of monocrotophos. With the hitherto established linkage between esterase overproduction and organophosphate tolerance in insects and the observed similarity in response of the insects and B. bassiana to the chemical, it is concluded that tolerance to monocrotophos in B. bassiana may be due to a mechanism similar to that operating in insects. Habituation of the fungus to monocrotophos to initiate expression of esterase gene may help in achieving compatibility between the two.