Dissertation Research: Insect Selection on Tropane Alkaloids

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9623387 Bergelson Plants are known to produce a wide variety of chemical compounds, some of which are used in medicine today. Many theories explaining the diversity of these compounds propose that plants produce them as defenses against herbivorous insects, but there is little experimental work to demonstrate the validity of this idea. This award will fund experiments to address the role of a particular class of plant chemicals, the tropane alkaloids, produced by members of the potato family (Solanaceae). Three strategies will be adopted to determine the functional importance of the major tropane alkaloids using two closely related members of the Solanaceae, deadly nightshade and jimson weed. The first approach is to add the alkaloids, both individually and in mixtures, to insect artificial diet in order to ascertain their effects on insect growth and survival. The second strategy is to test whether combinations or amounts of the alkaloids showing greatest toxicity to insect herbivores in the laboratory have a defensive function in natural populations. The final strategy is the most novel, and takes advantage of recent biotechnology to insert genes into plants. A gene for one of the enzymes necessary to create the alkaloids will be inserted into plants in the laboratory, qualitatively changing their alkaloid production. Individuals having these 'mutant' alkaloid profiles will be planted out in the field with ordinary or wild type plants, and the amount of damage and total seed production for plants of both kinds will be measured. This project has both implications for our understanding of the evolution of plant chemistry, and for the applied management of crmps. In particular, findings will help guide genetic engineering of more resistant plants and, in so doing, allow farmers to be less dependent on pesticide application.