The sweetpotato whitefly [Bemisia tabaci (Gennadius)] has become a high-risk insect pest in Mexico as well as in other countries, causing serious damage to several crops. Control of whitefly in Baja California Sur, ,Mexico, is usually done by intense insecticides applications, either alone or in mixtures of several kinds. The aim in this work was to determine its susceptibility to cypermethrin, endosulfan, methamidophos, and methyl-parathion. LC50 was obtained to identify the resistant and susceptible populations. A group of 20 whiteflies were introduced in a 20-ml scintillation vial coated in the inner surface with a known concentration of the insecticide. Mortality readings were obtained 3 h after exposing the insects to the residual activity at five concentrations. Five replications and control were run in different consecutive days for each bioassay. Results indicated that cypermethrin was the most toxic to B. tabaci and metamidophos the least. Data will be considered for further evaluations.
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