Tiger swallowtails use a number of plant species that vary in their chemical composition. These host species differ in their attractiveness to egg-laying females and their suitability for caterpillar growth. In addition, genetically different individuals show dissimilar responses on identical host plants. Potentially, the differential ability of swallowtails to recognize or grow on different plant species serves to maintain much of the genetic variation observed in natural swallowtail populations. Although selection tends to eliminate certain genotypes on certain hosts, it tends to increase their frequency on other hosts. The proposed research is designed to assess the genetic basis for the physiological and behavioral patterns of host plant usage by the tiger swallowtail. The investigators hypothesize that this subspecies is comprised of a complex of differentially adapted genotypes and populations. Experiments will compare the responses of three geographic populations and families within populations on three different host plants. Complementary analyses will determine the genetic substructure of these populations. Information obtained from these laboratory and field studies will elucidate the role of host diversity in maintaining genetic variability among and within populations of a single species. Such knowledge will help in understanding how insects adapt to their food sources and will prove useful in developing pest management programs for commercially important crop species.
