POWELL, J.S.*; RAFFA, K.F.: The effect of feeding specificity on the fate of terpenoids in Lymantriidae (Lepidoptera)

Insect herbivores possess a wide array of mechanisms for processing ingested phytochemicals. However, it is difficult to predict the fate of phytochemicals since it is influenced by many factors. We are testing whether feeding specificity influences the relative extent to which an herbivore relies on excretion, sequestration, and metabolism. Our model consists of 5 generalist and specialist Lymantriids, each of which include conifer terpenes within its diet. The monoterpenes bornyl acetate, limonene, and myrcene, and the diterpenes isopimaric acid and neoabietic acid all occur in tamarack, a common coniferous host of the 5 Lymantriid species. Each species is fed known amounts of these compounds in amended diet. Frass, larvae and exuviae are analyzed to quantify excretion and sequestration. Enzyme inhibitors are used to determine whether specific enzymes are responsible for metabolism. The fate of monoterpenes has been examined in 4 species. Preliminary results suggest metabolism is the most important mechanism for processing monoterpenes. Limonene and myrcene appear to be completely metabolized. Borneol, a metabolite of bornyl acetate is recovered in frass, larvae, and exuviae. Piperonyl butoxide does not affect recovery of any monoterpene or performance of larvae, indicating P450 enzymes are not responsible for metabolizing these monoterpenes. Excretion appears to be partially involved in processing bornyl acetate, but not limonene or myrcene. Both bornyl acetate and borneol are recovered from frass. The extent of each mechanism in processing monoterpenes depends on both the larval stadium and terpene concentration.