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 anisopliae, are insecticidal but comparatively low doses have antifeedant properties. Treatment of cabbage leaf discs with destruxins significantly reduced feeding by larvae of Plutella xylostella and Phaedon cochleariae in both choice 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 combination of the starvation and toxicity effects of destruxins. In whole plant experiments, adults and larvae of P. cochleariae were found to be more susceptible to infection by M. anisopliae V245 if it was used in conjunction with a crude destruxin mixture. Destruxins drove larvae off the plant, irrespective of which leaf surface was treated. Adults could be forced to the adaxial or abaxial surface of leaves using the crude destruxin. Mortality was usually more consistent and generally greater if adults were forced to abaxial than adaxial surfaces inoculated with the fungus. High humidity on the abaxial surface favoured conidia germination and infection. Mortality was also greater for adults dusted with the pathogen and forced to the abaxial rather than to the adaxial leaf surface. The increased movement and starvation associated with destruxin treatment may also have stressed the insects making them more susceptible to infection.     

Application of Metarhizium flavoviride (Deuteromycotina: Hyphomycetes) Spores Against the Tree Locust, Anacridium melanorhodon (Orthoptera: Acrididae), in Sudan

Spores of the entomopathogenic fungus Metarhizium flavoviride were applied against the tree locust Anacridium melanorhodon melanorhodon in the field for the first time. The treated areas covered a total of 55 ha in the vicinity of Tendelti in the White Nile State of Sudan. At a dose of 100 g of spores/ha applied in 5 l of oil formulation, the application led to a reduction in population densities of 66-76% after 18 days. Correction of the data with the Henderson/ Tilton formula gave an overall control efficiency of 68%.