Does escape to enemy-free space explain host specialization in two closely related leaf-feeding beetles (Coleoptera: Chrysomelidae)?

Abstract

This paper examines the role of predation and parasitism in the host specialization of two chrysomelid beetles that are monophagous on different species of Asteraceae. Ophraella notulata and O. slobodkini are sister taxa that feed on Iva frutescens and Ambrosia artemisiifolia respectively. Ambrosia is the purported ancestral host plant for this species pair. The question addressed is whether there is evidence that escape to enemy-free space may influence the host specialization of O. notulata on I. frutescens. I estimated egg predation, successful egg hatch, and larval parasitism directly, and larval predation indirectly, based on relative abundances of predatory insects and spiders. Egg predation was significantly higher on O. slobodkini and this was not due to species-specific differences in egg defense. However, egg hatch was not significantly different between O. notulata and O. slobodkini. Predatory arthropods were 4 times more abundant in A. artemisiifolia habitat than in I. frutescens habitat. Interestingly, larval parasitism by a tachinid fly was significantly greater on O. notulata than on O. slobodkini, opposite to the egg predation data and the inferred larval predation rate. There is little evidence to suggest that escape to enemy-free space is a factor that maintains the monophagy of O. notulata.