The greenhouse whitefly, Trialeurodes vaporariorum, is an important greenhouse pest, and occasional pest of vegetable crops. This species affects the quality of ornamental plants and transmits viruses. Since the greenhouse whitefly developed resistance to most conventional pesticides, greenhouse growers began to rely heavily on imidacloprid, a neonicotinoid insecticide. In this study, we evaluated the development of resistance to imidacloprid by a population of greenhouse whitefly from the Michigan State University Horticulture greenhouses. We have also begun work to determine if resistance to imidacloprid confers cross-resistance to other neonicotinoid insecticides registered for use in the greenhouse. Results of this work will help determine management strategies for imidacloprid-resistant whiteflies, and perhaps other imidacloprid resistant insects.