SILPHINENE DERIVATIVES - THEIR EFFECTS AND MODES OF ACTION ON COLORADO POTATO BEETLE

The silphinene derivatives 11 beta-hydroxy-5 alpha-(angeloyloxy)silphi nen-3- and 11 beta,5 alpha-dihydroxysilphinen-3-one were generated by means of chemical hydrolysis of the natural antifeedant and toxic silp hinene 11 beta-acetoxy-5 alpha-(angeloyloxy)silphinen-3- and bioassaye d against Colorado potato beetle larvae (Leptinotarsa decemlineata). B oth compounds showed significant antifeedant activity against this ins ect in choice and no-choice assays. Futhermore, exposure of larvae to these compounds over a 24 h period resulted in reduced feeding and gro wth rates. To distinguish between antifeedant and toxic effects, growt h efficiencies were calculated as the slope of the regression of relat ive growth rate on relative consumption rate. The comparison of these results with those of antifeedant simulation bioassays indicates that strong feeding inhibition is associated with the 11-acetate substituen t, while negative effects on larval growth through contact toxicity ar e related to the lipophilicity of the compounds. These substances were also bioassayed against three species of the plant pathogen Fusarium. The natural silphinene and the two derivatives showed mild antifungal activity inversely related to their polarity.