An Insect Model for Physiology of Taste Plasticity

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This research is designed to examine the physiological processes that occur during development and suppression of the sense of taste. Previous studies of taste development and modification have been severely handicapped by a lack of suitable animal models and a lack of known chemical compounds. Our recent discovery of diet-dependent taste sensitivity and development in a caterpillar suggests that this insect may serve as an ideal model. Newly hatched larvae of the cabbage butterfly are insensitive to bitter feeding deterrents present in unacceptable plants, but taste sensitivity develops as they feed on a suitable food plant such as cabbage. At the same time, larvae feeding on cabbage become dependent on, or addicted to specific chemicals for continued feeding. However, when the larvae are reared on a wheat germ artificial diet, development of sensitivity to deterrents and dependence on stimulants never occurs. Two major questions need to be answered before this model can be fully utilized. (1) To what extent are taste receptors involved in the modified ability of animals to taste? (2) What are the compounds in wheat germ that are responsible for taste suppression? We propose to answer these questions using behavioral tests after selective removal of known taste receptors from sensitive larvae. The involvement of these receptors will be confirmed by electrophysiological recordings from taste hairs of individual insects as their sensitivity to stimulants and deterrents develops. Behavioral assays also will be used to monitor isolation and identification of the active compounds from wheat germ. This work is expected to pave the way for more detailed studies of the biochemical processes involved in molecular recognition of specific food constituents as well as the development of cravings and addiction. If these taste hairs are in fact involved in sensitivity changes, the results are expected to help in explaining development and loss of taste in humans. The availability of an insect model may serve to eliminate or reduce the use of higher animals for clinical testing, and information about dietary experience that can influence food choice by insects could have significant agricultural importance in the design of new pest management strategies.