Chemical Ecology of Swallowtail Butterflies

Cornell Univ - State: Awds Made Prior May 2010, Ithaca NY

Investigators

Abstract

The long-term goal of this research is to discover how chemical similarities and differences among plants have influenced associations between plants and the insects that feed on them. Most plant-feeding insects are specialists, feeding and laying their eggs on only a few plant species. They find and identify their particular food plants largely by smelling characteristic odors produced by the plants or by tasting characteristic mixtures of chemical compounds in the plant tissues or on the plant surfaces. Indeed, plant species that are attacked by a particular species of insect typically share one or more kinds of unusual chemical compounds. This suggests that the ability of insects to add new plant species to their diet is facilitated by the shared occurrence of particular compounds. The swallowtail butterflies (family Papilionidae) are used as a model system in this research because their classification and larval food plants are especially well known. During the next three years, the PIs plan to concentrate on the black swallowtail (Papilio polyxenes) and to determine why females of this species almost never lay their eggs on plants outside the carrot family (Apiaceae) and yet accept a wide range of different species within this family. At least in part, females identify plants on which to lay their eggs by detecting stimulant compounds with taste receptors on their feet and by odor receptors in their antennae. Several of these stimulant compounds have already been identified. The PIs will complete the identification of these stimulants for the black swallowtail in three common host species, namely carrot, wild parsnip, and poison hemlock. The PIs will then determine whether the mixtures of stimulants share compounds in common or whether each plant is recognized by a different set of stimulant compounds. Preferences of individual black swallowtail females among the three food-plant species will be compared with preferences for stimulant extracts to determine whether these are primarily responsible for host preference among different species. The PIs will measure variation in the preferences of individual females and raise their progeny so that the PIs can compare the corresponding preferences of their female offspring. These experiments will tell us whether variation among females results, at least in part, from inherited differences in responses to chemical cues. Despite recent progress, mostly in Europe and Japan, remarkably little is known of the chemical mixtures by which insects recognize their host plants, let alone of the genetics underlying the relevant sensory mechanisms. This research should contribute to the basic knowledge required for the wise deployment of new crop varieties whose chemistry has been modified by genetic engineering.