A population of greenhouse whitefly Trialeurodes vaporariorum, which had been treated on numerous occasions with imidacloprid prior to 2000, has been cultured in a section of the Plant Science Greenhouses at Michigan State University. A standard insecticide efficacy test was conducted in 2003 and the result showed a failure of imidacloprid applied as a soil drench at the labeled rate for whitefly control. Subsequently, a significant reduction of resistance to this insecticide was observed in the same population in 2006. The toxicity of other neonicotinoid insecticides to the greenhouse whitefly was also evaluated by using a systemic uptake bioassay method. The use of these insecticides on whitefly insecticide resistance management is discussed.