63-68The growth inhibitory activity and
deterrency of Melia dubia (Meliaceae) extracts to Spodoptera litura and
Helicoverpa armigera were investigated. Artificial diet bioassays using
neonate larvae of both S. litura and H. armigera indicated
that dichloroethane (DCE) and methanol (Me) extracts of M. dubia inhibited
growth in a dose dependent manner. DCE and Me-5II fractions also
resulted in 50% deterrency at concentrations of 22.5 and 16.8 μg/cm2
respectively against S. litura larvae in a leaf disc-choice
test. The DCE-5 fraction was found to be more toxic to larvae (LC50 of 0.65%) than the Me-5II (LC50
of 0.8%), 72hr after topical application. Both fractions lack contact toxicity,
but the deterrent effect persisted for at least 60hr under laboratory
conditions. Although salannin was isolated from the DCE fraction to show
antifeedant activity, the physico-chemical characteristics of the active
fractions DCE-5 and Me-5II were not identical with either salannin or azadirachtin