Larval developmental rates of three putative subspecies of tiger swallowtail butterflies, Papilio glaucus, and their hybrids in relation to temperature.

The eastern tiger swallowtail butterfly, Papilio glaucus L. has been presumed to be comprised of three parapatric subspecies (P. g. canadensis R & J, across Canada and the northern U.S.; P. g. glaucus L., in the eastern half of the U.S.; and P. g. australis Maynard, in Florida). Populations from 27° north latitude in Florida to 50° north latitude in Manitoba, Canada and from 75° west longitude in Pennsylvania to 96° west longitide in Canada were tested by laboratory larval feeding studies at various constant temperatures ranging from 16°-28° C. These data indicate that populations of Papilio glaucus show generally similar developmental responses to temperature, regardless of their geographic origin. Limited differences do exist between some populations studied, involving such traits as upper threshold temperature and differences between individual developmental rate curves. No consistent differences were noted between the three putative subspecies in their developmental response under these experimental conditions. In Wisconsin, the twenty year average of total season degree day accumulations above a base temperature (developmental threshold) of 10° C delineates a relatively narrow geographical region across the center of the state for which the bivoltine potential reaches its northernmost limits. This zone also closely corresponds to the southernmost limit of the P. g. canadensis subspecies (generally believed to be obligately univoltine).