Effects of ajugarins and related neoclerodane diterpenoids on feeding behaviour of Leptinotarsa decemlineata and Spodoptera exigua larvae

Three naturally occurring ajugarins and seven semisynthetic derivatives of them, possessing different functionalities in the decalin part, together wi th two natural furoneoclerodane diterpenes, have been assessed as feeding b ehavior modifying agents of larvae of the generalist Spodoptera exigua and a specialist like Leptinotarsa decemlineata. Ajugarin I and some of its der ivatives exhibited a significant antifeedant activity against larvae of S. exigua in both choice and no-choice assays. Conversely, the furoneoclerodan e diterpenes only presented antifeedant activity against larvae of L. decem lineata. These results indicate that the biological action of the tested su bstances is strongly modulated by minimal structural variations, which are also responsible for the specificity of action. (C) 2001 Elsevier Science L td. All rights reserved.