Silphinene sesquiterpenes are established chrysomelid antifeedants. In this work, nine silphinene analogs, 11-acetoxy-5-angeloyloxysilphinen-3-one (
1), 11-acetoxy-5-tigloyloxysilphinen-3-one (
2), 11-acetoxy-5-iso- butyryloxysilphinen-3-one (
3), 11-hydroxy-5-angeloyloxysilphinen-3-one (
4), 11,5-dihydroxysilphinen-3-one (
5), 11,5-diacetoxysilphinen-3-one (
6), 5,11-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.
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