Antifeedant properties of destruxins and their potential use with the entomogenous fungus Metarhizium anisopliae for improved control of crucifer pests

Destruxins A, B and E, produced by the entomogenous fungus Metarhizium anis opliae, me insecticidal but comparatively low doses have antifeedant proper ties. Treatment of cabbage leaf discs with destruxins significantly reduced feeding by larvae of Plutella xylostella and Phaedon cochleariae in both c hoice and no-choice assays The Antifeedant Index (AI) was dose related and there were significant differences between treated and untreated leaves The AI and acute toxicity assays suggest that insect death was due to a combin ation of the starvation and toxicity effects of destruxins. In whole plant experiments, adults and larvae of P. cochleariae were found to be more susc eptible to infection by M. anisopliae V245 if it was used in conjunction wi th a crude destruxin mixture. Destruxins drove larvae off the plant, irresp ective of which leaf surface was treated. Adults could be forced to the ada xial ol abaxial surface of leaves using the crude destruxin. Mortality was usually more consistent and generally greater if adults were forced to abax ial than adaxial surfaces inoculated with the fungus. High humidity on the abaxial surface favoured conidia germination and infection. Mortality was a lso greater for adults dusted with the pathogen and forced to the abaxial r ather than to the adaxial leaf surface. The increased movement and starvati on associated with destruxin treatment may also have stressed the insects m aking them more susceptible to infection.