Starting from precocenes I and II, four of their derivatives with a lactone moiety were obtained. The compounds have been assessed as antifeedants against several diverse insect species including the storage pests the confused flour beetle (Tribolium confusum Duv., larvae and adults), the granary weevil beetle (Sitophilus granarius L., adults), and the khapra beetle (Trogoderma granarium Ev., larvae) and against the herbivorous pest insects Colorado potato beetle (Leptinotarsa decemlineata Say, adults and larvae) and aphids (Myzus persicae Sulz.). Precocenes, especially precocene II, showed a very strong antifeedant effect against all storage pests and aphids. The introduction of a lactone moiety caused a decrease in antifeedant activity against these species. Both precocenes were moderately active against L. decemlineata adults. The best antifeedants to this species were precocene derivatives, especially iodolactones. The introduction of iodine into a molecule had a great effect on the antifeedant activity of those compounds.