PATTERNS OF HERBIVORY IN THE QUERCUS-GRISEA X QUERCUS-GAMBELII SPECIES COMPLEX

In a recent paper, Whitham proposed the hybrids-as-sinks hypothesis, which posits that hybrid hosts are more susceptible to phytophagous insects than are parental hosts. We test the hybrids-as sinks hypothesis in the Quercus grisea Liebm. X Quercus gambelii Nutt. hybrid complex. We measure densities of leaf-mining moths (Lepidoptera: Nepticulidae and Gracillariidae) and gall wasps (Hymenoptera: Cynipidae) on parental and hybrid host trees. We find no support for the hybrids-as-sinks hypothesis in the present hybrid complex. Hosts in this complex exhibited a unidirectional herbivore gradient, where hybrid hosts supported intermnediate levels of herbivores when compared to parental species. We discuss possible causes affecting patterns of herbivore densities and distribution in this species complex, including host architecture, leaf morphology, and geographic range.