You are what you eat: native versus exotic Crotalaria species (Fabaceae) as host plants of the Ornate Bella Moth, Utetheisa ornatrix (Lepidoptera: Erebidae: Arctiinae)

Abstract

Crotalaria plants and Utetheisa ornatrix are closely linked to each other: the larvae destroy the seeds, while the moth depends on hostplants for alkaloids. To better understand the ongoing co-evolution, the present study examines how native hostplants compare to exotic ones. Leaf-feeding on Crotalaria pumila, C. rotundifolia, and C. incana, native to the moth’s range, led to faster larval development than on the exotic C. lanceolata, C. spectabilis, and C. pallida. Seed-feeding on all species of Crotalaria led to accelerated larval development and a resultant larger adult moth, and correlates with a higher nitrogen content in the plant tissues. These results add a novel dimension to the previous studies of reproductive biology of this model organism. In controlled settings, mature larvae showed preference for leaves of C. spectabilis over those of other species, perhaps due to the higher alkaloid content. Differences in morphology and phenology of Crotalaria determine the ecology of U. ornatrix populations in Florida. The introduction of novel hostplants, on which U. ornatrix can have a significant negative effect and which are of concern to humans as invasive toxic weeds, has greatly expanded the niche occupied by this moth. Possible co-evolution of Utetheisa sensu lato and plant defences in the genus Crotalaria is discussed.

Keywords:

• chemical defence
• pyrrolizidine alkaloids
• trophic interactions
• invasive exotic weeds
• biological control
• plant–herbivore co-evolution

Acknowledgements

I thank Alexandra Pagac, Mykhue Nguyen-Tran, Jim Grantham, and Beth Currey for their help in preparing voucher specimens; Eric Anderson and Andrew Bliss for their help with propagating plants; Eric Anderson also for serving as a companion and guide on several Crotalaria-finding trips in north Florida; Matthew Standridge for finding seeds of C. rotundifolia and collecting moths at the Cross Creek site; Alexandra and Nika Sourakov for proofreading the manuscript and offering many helpful suggestions; and the anonymous reviewers, whose comments helped to greatly improve the manuscript.