FOOD UTILIZATION AND ANTIOXIDANT ENZYME-ACTIVITIES OF BLACK SWALLOWTAIL IN RESPONSE TO PLANT PHOTOTOXINS

Phototoxic compounds are widely distributed among plant families; due to their ability to bind covalently to DNA or to react with oxygen and generate toxic oxyradicals, these compounds are toxic to a variety of herbivorous organisms. Black swallowtail (Papilio polyxenes) larvae feed exclusively on phototoxic host plants in the Apiaceae and Rutaceae. In this study, we examined the toxicity of four phototoxins-three furanocoumarins and one beta-carboline alkaloid-to P. polyxenes, as well as the inducibility of antioxidant enzyme defenses in response to these phototoxins. Neither the furanocoumarins nor the beta-carboline alkaloid demonstrated any toxic effect on digestive efficiencies of P. polyxenes in the presence of light; harmine, the alkaloid, did significantly reduce growth and consumption rates. None of the compounds had a significant effect on antioxidant enzyme levels. These findings contrast with those reported in earlier studies for Trichoplusia ni, a generalist noctuid sensitive to both furanocoumarins and beta-carboline alkaloids. Greater detoxicative metabolic capabilities, coupled with substantially higher constitutive levels of antioxidant enzyme activity, likely explain at least in part the absence of induced antioxidant enzyme responses in the specialist feeder on phototoxic plants.