A method to distinguish between the adults of two important agricultural pests, Bemisia tabaci (Gennadius) and Trialeurodes vaporariorum (Westwood), has been established by means of microscopic examination of compound eyes. A field survey using this method showed this method could distinguish the two hitefly species rapidly and reliably. The method showed that the upper and lower compound eyes of B.tabaci were connected by one ommatidium, while the upper and lower compound eyes of T.vaporariorum were completely divided.