Plant poisons in a terrestrial food chain.

Abstract

By the selection of a strain of cabbage-eating monarch butterfly larvae, Danaus plexippus, it has been possible to show experimentally that this nonpoisonous food plant renders larvae, pre-pupae, and adult monarchs palatable to blue jays. Monarchs reared on Asclepias curassavica, a natural food plant known to contain heart poisons, caused the same birds to vomit, even following the ingestion less than 1 adult. Another asclepiad plant (Gonolobus rostratus), lacking cardiac toxins, proved to produce fully palatable adults. It was concluded that the unpalatability of the monarch butterfly is causally related to the species of plant ingested by the larvae. Although direct transfer of poisonous molecules from plant to insect is strongly suggested, radioactive labeling would provide the only direct proof. The discovery of an intraspecific palatability poly morphism in the monarch butterfly prompts us to advance a new theoretical category of mimicry: automimicry.