Pathogenicity Enhancement of Metarhizium anisopliae and Beauveria bassiana to First Instars of Diaprepes abbreviatus (Coleoptera: Curculionidae) with Sublethal Doses of Imidacloprid

Abstract

Beauveria bassiana (Balsamo) Vuillemin and Metarhizium anisopliae (Metschnikoff) Sorokin combined with sublethal doses of imidacloprid as a contact or oral treatment increased synergistically mortality and mycosis of 1st instars of Diaprepes abbreviatus (L.). Time to death was also reduced significantly through the synergistic effect of the fungal/chemical treatment. Synergism only occurred at concentrations of imidacloprid of 100 ppm or greater. At fungal concentrations of 106 and 107 conidia per milliliters and imidacloprid at doses of 100 ppm or greater, larval mortality and mycosis reached 90–100%. Mycosis was reduced with imidacloprid at 1,000 ppm. There were no differences in larval mortality or mycosis by M. anisopliae when imidacloprid was administered by contact or per os. The active ingredient rather than the inert carrier was the main component responsible for the synergism between imidacloprid and entomopathogenic fungi.