| The furocoumarin xanthotoxin and the furoquinoline alkaloid skimmianine, both widespread in rutaceous plants, were fed to butterflies in the family Papilionidae. The representative Papilionini, Papilio polyxenes and Papilio cresphontes, ingested the two allelochemicals without detrimental effect while the representative Troidini, Battus philenor, experienced reduced consumption and survival, and the representative Graphiini, Eurytides marcellus, suffered symptoms of complete toxicity. Since the Troidini are more closely related to the Papilionini than either is to the Graphini, these results demonstrate that metabolic similarities reflect phylogenetic relationships. These results also demonstrate that xanthotoxin and skimmianine are important feeding barriers to non-adapted insects.;The skimmianine used for bioassay was extracted and purified from Zanthoxylum americanum. Bioassays of skimmianine with Heliothis zea, a polyphagous noctuid, demonstrated that skimmianine was present in the most toxic fraction of Z. americanum, and that pure skimmianine is acutely toxic to H. zea at 0.1% fresh weight.;Xanthotoxin present in host plants of Papilio polyxenes prevents establishment of some bacteria in the gut, but other bacteria are xanthotoxin-tolerant and increase in relative proportion in the xanthotoxin-enriched medium of the macerated food. When Papilio polyxenes consumes a different host plant with low levels of furocoumarins there is no enrichment in the proportion of xanthotoxin-tolerant types.;The foliage of one host plant, Pastinaca sativa, has far greater numbers of bacteria than another host, Petroselinum sativum, but when caterpillars consume the foliage of either plant the numbers of bacteria that survive in the gut are equivalent. This suggests that the environment of the caterpillar gut controls bacterial densities regardless of initial numbers consumed with the food.;Streptomycin administered as a solution into which the cut ends of parsley sprigs are immersed is consumed by Papilio polyxenes when the caterpillars eat the saturated foliage. Assays of the total number of gut bacteria of these caterpillars indicated that short-term ingestion of streptomycin exhibited dose-dependant antibacterial effects in the gut. Long term ingestion of streptomycin caused mortality in caterpillars, but the few survivors contained streptomycin-tolerant bacteria, and contained greater numbers of streptomycin-tolerant bacteria when they were feeding on plants with greater concentrations of streptomycin. |
