Tropical Timber Species as Sources of Botanical Insecticides

Screening of wood extractives from tropical timber species and other trees against pestiferous lepidopterans such as the tobacco cutworm, Spodoptera litura and the variegated cutworm, Peridroma saucia, indicates the presence of insecticidal and growth inhibitory factors in certain genera. The mahogany family (Meliaceae)includes several important timber species in the genera Swietenia, Khaya, Cedrela and Entandophramgma, but also includes the Indian neem tree, Azadirachta indica, already well-known as a source of potent botanical insecticides. Strong bioactivity against insects has been observed in extracts from species of Aglaia, Trichilia and Chisocheton. In most cases, limonoid triterpenes, characteristic secondary metabolites of the Meliaceae, are responsible for bioactivity, but in the case of Aglaia, the insecticidal principles are modified benzofurans. Extractives from several genera of the African walnut family (Olacaceae)have potent bioactivity as larval growth inhibitors, but this family has had sparse chemical characterization to date. Extractives from the Dipterocarpaceae, the most important family of timber species in tropical Asia, were essentially inactive in our screening program. However, bark, woodwaste and sawdust from certain commercially harvested timber species could be exploited for their biologically-active constituents