LACK OF EVIDENCE FOR THE TOXIC NECTAR HYPOTHESIS - A PLANT ALKALOID DID NOT DETER NECTAR FEEDING BY LEPIDOPTERA

Floral nectars of many plant species contain alkaloids and other allel ochemics that might deter butterfly visitors and promote flower consta ncy by specialized pollinators. The pyrrolizidine alkaloid, monocrotal ine, has been implicated as such a feeding inhibitor in nectar, in sup port of this toxic nectar hypothesis. We tested this hypothesis by eva luating monocrotaline for deterrence of nectar feeding in the tobacco budworm moth, Heliothis virescens (Fab.), the cabbage looper moth, Tri choplusia ni (Hubner), and the gulf fritillary butterfly, Agraulis van illae (L.). Concentrations of monocrotaline added to aqueous sucrose s olutions did not reduce consumption in these three species, even with near saturation concentrations of monocrotaline. Also, gulf fritillary butterflies did not alter their preference for visiting orange artifi cial flowers when given the choice between yellow flowers with a sugar solution and orange flowers with a monocrotaline and sugar solution. Patterns of flower visitation by Lepidoptera are likely due to a combi nation of factors, such as attractants, feeding stimulants and deterre nts, visual stimuli, flower morphology, and ecological factors that co ntrol nectar availability.