PL-2
INSECT DEFENCES OF TROPICAL AND TEMPERATE AMERICANFAMILIES
J.Thor Arnason1, Tony Durst1 and Pablo Vindas-Sanchez2
1Faculty of Science, University of Ottawa, Ottawa, CanadaK1N 6N5
2 Universidad Nacional, Heredia, Costa Rica.
Our phytochemical discovery program has undertaken a search forsearch for novel phytochemicals affecting insect behavior, growth and development in selected plant families of the Americas. Over 50 extractsof tropical Meliaceae were screened for growth reducing and antifeedantactivity to lepidoptera. The genus Trichilia was especially activeand new limonoids and steroids have been obtained from the genus. A relatedbut rare tropical family, the Lepidiobotyaceae has afforded over 12 completelynovel, but structurally related C,D spiro triterpenoids. The redundancyof these compounds has been shown to be a more effective defence than singlecompounds. The Piperaceae and Asteraceae have also provided several novellignans that modulate PSMO activities and the p-glycoprotein mediated toxinpump that allows insects and other organisms to excrete xenobiotics. Mixturesof phytochemical types co-occurring in these plant families is proposedas a constraint on the evolution of tolerance in adapted herbivores.