Abstract
The silphinene derivatives 11β-hydroxy-5α-(angeloyloxy)silphinen-3-one and 11β,5α-dihydroxysilphinen-3-one were generated by means of chemical hydrolysis of the natural antifeedant and toxic silphinene 11β-acetoxy-5α-(angeloyloxy)silphinen-3-one and bioassayed against Colorado potato beetle larvae (Leptinotarsa decemlineata). Both compounds showed significant antifeedant activity against this insect in choice and no-choice assays. Futhermore, exposure of larvae to these compounds over a 24 h period resulted in reduced feeding and growth rates. To distinguish between antifeedant and toxic effects, growth efficiencies were calculated as the slope of the regression of relative 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 substituent, while negative effects on larval growth through contact toxicity are 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. Keywords: Leptinotarsa decemlineata; Coleoptera Chrysomelidae; antifeedant; toxic; silphinene derivatives
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