Influence on Larval Growth of the Eastern Black Swallowtail Butterfly Papilio polyxenes (Lepidoptera: Papilionidae) of Seasonal Changes in Nutritional Parameters of Umbelliferae Species

Larvae of the eastern black swallowtail butterfly, Papilio polyxenes asterias (Stoll) were fed a variety of plants of the family Umbelliferae and were analyzed for larval growth, feeding efficiencies and nitrogen budgets as a function of food plant age and nutrient content. Several food plants (Hydrocotyle americana, Sanicula gregaria, Osmorhiza claytoni, Osmorhiza longistylis and Torilis japonica of the Umbelliferae; and Xanthoxylum americanum of the Rutaceae) proved to be unacceptable to the larvae in no-choice situations for a variety of reasons. Among these, we found escape in space, escape in time, and a newly discovered physical trichome defense of Torilisjaponica to be involved. The food plants suceessfully fed upon (Daucus carota, Pastinaca sativa, Conium maculatum, Cicuta bulbifera, Angelica atropurpurea, Thaspium trifoliatum, Cryptotaenia canadensis, Chaerophyllum procumbens, and Heracleum maximum) showed significant seasonal differences in their nutritional value as food for Papilio polyxenes larvae. An analysis of both the nutrient composition of the plant and the insect utilization indices upon each food plant showed no consistent seasonal trends in plant "quality. " Instead, the leaves of each plant species varied in their nutritional value (nitrogen and water contents) according to its own particular phenology. Larvae fed on plants which had low leafwater contents (less than 759%) were unable to increase their assimilation or nitrogen utilization efficiencies enough to maximize growth rates. Larvae on certain low-water plants achieved higher consumption rates, but this could not adequately compensate for the low efficiency of assimilation and utilization efficiency of plant biomass and nitrogen, so growth rates remained low. INTRODUCTION Phylogenetic constraints upon the adaptations of herbivores to their food plants remain poorly understood (Diehl and Bush, 1984; Futuyma and Peterson, 1985). Local specialization upon preferred food plants appears to be the rule rather than the exception in Lepidoptera (see reviews in Wiklund, 1975; Fox and Morrow, 1981; Scriber, 1983, 1986a, 1986b; Scriber et al., 1986). The North American Umbellifer-feeding swallowtail butterflies are no exception, and local oviposition favorites are known to exist (Scudder, 1889; Heitzman, 1973; Emmel and Shields, 1978; Scriber and Finke, 1978; Blau, 1980; Shapiro and Masuda, 1980; Sims, 1980a, 1980b; Wiklund, 1981; Goeden and Ricker, 1982; Jackson, 1982; Opler and Krizek, 1984; Feeny et al., 1985). Leaf nutritional quality can be a driving force in the growth rate of insects, and seasonal variation in leaf chemistry can have dramatic effects upon insect preference/ performance (Feeny, 1970; Scriber, 1977; Scriber and Slansky, 1981). This study was designed to delineate the suitability of the species of Umbelliferae over the course of the growing season in Greene County, Ohio, to the umbellifer-feeding specialist, Papilio polyxenes. Specifically, we determined the effects of seasonal variation in leaf quality upon the consumption rates and efficiencies of leaf tissue processing for larval growth 'Current address: 1028 Labonne Parkway, Valley Park, Missouri 63088. 2Current address: Department of Entomology, Michigan State University, East Lansing 48824. 3Send reprint requests to J. M. Scriber.