Insect antifeedant activity of clerodane diterpenoids against larvae ofSpodoptera Littoralis (Boisd.) (Lepidoptera)

Antifeedant activities of nine clerodane diterpenoids, isolated in this laboratory from different species ofAjuga plants, have been studied against larvae of Egyptian cotton leafwormSpodoptera littoralis (Boisd.) (Lepidoptera) by application of the leaf disk method. Evaluation of activity was carried out by calculating, at different time intervals, the feeding ratio (FR) from the relationship between the consumed areas of treated disks (CTD) and control disks (CCD); for comparison purposes a FR50 defined as the FR at a CCD of 50% was established. Some compounds exhibited activity at a 0.01 μg/cm(2) dose (0.3 ppm). Structure-activity relationships are discussed.