Potential host plants of Trirhabda geminata (Coleoptera: Chrysomelidae): impacts on survival, development, and feeding.

Although larvae and adults of the herbivorous beetle Trirhabda geminata Horn (Coleoptera: Chrysomelidae) are primarily considered to be specialists on Encelia farinosa (Compositae: Asteraceae), some reports exist of these beetles feeding on related Encelia species. Within the genus Encelia, many species are thought to have evolved relatively recently. In addition, some Encelia species have very similar secondary chemistries and overlapping geographic distributions. In the laboratory, individual T. geminata were reared on E. farinosa or the sympatrically occurring species E. actoni or E. californica. Survival, growth, and development were analyzed for larvae feeding on each host plant species. Overall, herbivore performance was better on E. farinosa, with significantly greater survival, faster development, and greater mass gain. Beetle development on E. californica was intermediate, with some measure, indicating better performance than on E. actoni and other measure, indicating no difference between these potential hosts. Importantly, although performance was decreased on E. actoni and E. californica, some individuals were able to develop successfully, suggesting that populations of T. geminata may be able to adapt to use these host plants.