THE ANTIFEEDANT PROPERTIES OF T. AMERICANA

Deborah A. Wheeler and Murray B. Isman
Department of Plant Science, University of British Columbia, Vancouver,Canada V6T 1Z4.

Screening of plants in the Meliaceae family for insecticidal activityhas lead to many promising leads in the search for new botanical insecticides.In the genus Trichilia one species, T. americana has beenfound to be particularly active against the Asian armyworm, Spodopteralitura. Several bioassays have been used to assess the activity andmode of action of crude methanol extracts of wood. Most activity has beenfound in small twigs, with an EC50 (effective concentration to reducegrowth by 50%) of 15ppm. Choice leaf disc assays have shown strong antifeedantactivity, with 100% inhibition of feeding at a concentration of 1?g/cm2leaf disc. Nutritional assays looking at indices such as relative growthrate (RGR) and relative consumption rate (RCR) indicate that activity ismainly through deterrency, with large reductions in RCR. Bioassays investigatingpossible chronic toxicity and insect growth regulatory effects are in progress.Isolation of the active compound(s) is also being carried out.