Dr. Messina's research is aimed at elucidiating the behavioral mechanisms by which an insect chooses its food plants. Whether a particular insect will become a serious pest or not depends on its response to a series of physical and chemical traits associated with its potential hosts. Some insects are known to avoid laying eggs on plants if those plants already bear eggs; chemical "marking pheromones" are typically used by egg-laying females to distinguish between occupied and unoccupied hosts. Several investigators have suggested that these natural deterrents to egg-laying may eventually provide an additional tool in pest management. Dr. Messina is investigating the behavioral sequence involved in rejecting or accepting a host on the basis of whether or not other insects are already present on it. The research also attempts to understand the high degree of variation in egg-laying behavior that has been observed among separate populations or "biotypes." Finally, the experiments will assess how egg-laying decisions are influenced by learning or experience, which has been largely ignored in insect studies. When combined with previous genetic and physiological data, the experiments should provide a thorough picture of an unusually complex invertebrate behavior. The seed beetle Callosobruchus maculatus is perhaps the most destructive pest of cowpea and related grain legumes in several regions of the world. It has been associated with human stores of legume seeds for at least a few thousand years. Female beetles are known to use a variety of cues in their host choices. The susceptibility of a legume variety is strongly affected, for example, by the texture of the seed coat. Predicting beetle behavior and population growth has been complicated, however, by extreme variation in several traits among different geographic populations. Dr. Messina's research will identify how variation in both larval and adult behavior affects the degree of competition between individuals and, in turn, the rate of population growth. In general, these studies provide a model system for understanding the origin and maintenance of life- history variation among populations of a single species.
