CONIDIAL ATTACHMENT OF METARHIZIUM-ANISOPLIAE AND BEAUVERIA-BASSIANA TO THE LARVAL CUTICLE OF DIAPREPES-ABBREVIATUS (COLEOPTERA, CURCULIONIDAE) TREATED WITH IMIDACLOPRID

A series of experiments was conducted to determine the effect of imida cloprid on the number of Metarhizium anisopliae and Beauveria bassiana conidia found on the cuticle of first instar Diaprepes abbreviatus fo llowing different treatments. Larvae treated with M. anisopliae conidi a and imidacloprid by dipping removed significantly fewer conidia from their cuticle when in contact with soil or a food source compared wit h fungal-treated larvae alone. In addition, more M. anisopliae and B. bassiana conidia were found on the cuticle of larvae treated with imid acloprid while exposed to soil at 7 and 14% moisture resulting in high er larval mortality and mycosis. Conidial attachment to cuticles of un treated larvae was higher at < 1% compared with 7 and 14% soil moistur es. M. anisopliae conidia were distributed uniformly over the pleural membrane of the larval cuticle of both untreated and imidacloprid-trea ted larvae. However, fewer conidia were attached to specific sites suc h as setae and setal sockets of treated larvae. At 12 h after treatmen t, imidacloprid-treated larvae had fewer conidia removed from exposed cuticle, setae, and spiracles than did untreated larvae. Cuticular exp osure to imidacloprid at doses >0.01% (AI) affected conidial attachmen t of M. anisopliae negatively. Conidial number decreased sevenfold at 0.1% (AI). Comparative data on the effect of imidacloprid formulation on conidial attachment showed that components of the inert ingredient were responsible for lower conidial attachment on larval cuticle at hi gher insecticidal doses. (C) 1998 Academic Press.