Biological Activity of Extracts of Trichilia Species and the Limonoid Hirtin Against Lepidopteran Larvae

Abstract

Crude extracts of several Trichilia species (Meliaceae) were evaluated for their behavioral and physiological effects on the polyphagous lepidopterans Peridroma saucia and Spodoptera litura. A majority of extracts of nine Trichilia species, collected primarily from Costa Rica, significantly deter larval growth of P. saucia. Extracts of wood and bark are generally more active than those of foliage. Effects of various tissue extracts from T. connaroides on P. saucia and S. litura were comparatively studied. Extracts of bark, the most active tissue compared to those of wood, seed, exocarp and leaf, reduced larval growth of P. saucia and S. litura by 50% at dietary concentrations of 29.1 and 185.1 ppm, respectively. The limonoid hirtin, a constituent of Trichilia hirta, significantly inhibited larval growth of P. saucia in a dose-dependent manner, with a dietary EC50 (effective concentration to inhibit growth by 50% relative to controls) of 13.0 ppm. Hirtin and various extracts from T. connaroides significantly reduced larval growth and consumption rates, as well as dietary utilization, indicating that these substances possess both behavioral effects and post-ingestive toxicity.