Plants and plant-feeding insects account for half of all known species, and it is widely thought that interactions between them have driven each group’s tremendous diversification. However, much remains unknown about how plant-insect interactions can generate new species. Does speciation in plants lead to co-speciation in plant-feeding insects, and if so, how? Tim studies these questions in the hot deserts of North America using creosote bush (Larrea tridentata) and the specialized community of creosote-feeding insects as a model system. His work combines field surveys across arid lands of the US and Mexico, behavioral experiments, and genetic approaches to characterize the links between plant and insect speciation.