Ecologists and evolutionary biologists have proposed speciation models for herbivorous insects that make critical assumptions about genetics, behavior, and ecological interactions with the host plants. Testing these assumptions will lead to an improved understanding of plant-herbivore interactions. If these assumptions are tested in populations that have recently diverged, or are in the process of diverging, these tests can help determine which of several competing models of speciation are most plausible. Hypotheses about these assumptions will be tested in two populations of a gall-making herbivore on two closely related host plants. These populations are of one morphological species and are partially reproductively isolated due to differences in host preference for mating and egg-laying. Knowledge of genetic and other mechanisms responsible for these preferences are crucial to understanding how herbivore speciation occurs. These questions will be explored with a series of field, experimental garden, and greenhouse experiments. Results from crosses between the host-associated populations will be used to determine how host-and mating-site preferences and the ability to survive different host plants is inherited. Additional experiments will be conducted to determine how environment and experience influence oviposition-and mating-site preference. Studies will also be conducted to determine how natural selection differs between host plants that could select for divergence of populations. Finally, whether there is genetic variation within one host-associated population could preadapt the behavioral for a shift to a new host plant will be investigated. Taken together, these data will provide insight into the ecology of plant-herbivore, interactions, the evolution of host expansions, speciation, as well as the specialized adaptations of agricultural pests.
