Silphinene sesquiterpenes as model insect antifeedants

Abstract

Silphinene sesquiterpenes are established chrysomelid antifeedants. In this work, nine silphinene analogs, 11beta-acetoxy-5alpha-angeloyloxysilphinen-3-one (1), 11beta-acetoxy-5alpha-tigloyloxysilphinen-3-one (2), 11beta-acetoxy-5alpha-isobutyryloxysilphinen-3-one (3), 11beta-hydroxy-5alpha-angeloyloxysilphinen-3-one (4), 11beta,5alpha-dihydroxysilphinen-3-one (5), 11beta,5alpha-diacetoxysilphinen-3-one (6), 5alpha,11beta-diisobutyryloxysilphinen-3-one (7), silphinen-3,5,11-trione (8), and O-methyl-5-epicantabrenolic acid methyl ester (10), and a presilphiperfolane sesquiterpene (9) were tested against several divergent insect species, including the lepidopteran Spodoptera littoralis, the chrysomelid Leptinotarsa decemlineata, and five aphid species, and their antifeedant effects were compared with those of picrotoxinin, a GABA-antagonist, and thymol, an allosteric modulator for insect GABA receptors. All insects tested responded to at least one silphinene analog and/or GABA antagonist. Compound 3 and thymol were effective antifeedants against all species tested except S. littoralis, with varying potencies according to their feeding ecologies. The toxicity of these compounds was species-dependent and did not correlate with their antifeedant effect.