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Whiteflies Bemisia tabaci and Trialeurodes vaporariorum cause high economic damage to commercial crops in Sri Lanka. Insecticide resistance was tested in B. tabaci collected from Kandy, Anuradhapura, Badulla, Matale and Hambantota districts and T. vaporariorum collected from Puttlam District against six insecticides using leaf dip bioassays. LC 50 values and percentage mortalities for the recommended dosages were determined by log-probit mortality curves. Metabolic resistance caused by increased activities of esterases, glutathione S-transferases and cytochrome P 450monooxygenases, and the insensitive target site resistance caused by acetylcholinesterases were evaluated by biochemical assays. Overexpression of CYP6CM1 monooxygenase protein in B. tabaci was tested using a lateral flow assay kit. The highest and the lowest resistance factors (RFs) were obtained for etofenprox (1311) and profenofos (4), respectively. Resistance percentages of whitefly populations to the recommended dosages were 37−83% for thiamethoxam, 50−83% for acetamiprid, 71% for imidacloprid, 2-36% for profenofos, 15-53% for carbosulfan and 68-89% for etofenprox. Anuradhapura, Badulla and Matale populations had elevated esterases, all populations had elevated GST activities and Badulla population had elevated monooxygenase activities. Populations were homozygous resistant or heterozygous for altered acetylcholinesterase mechanism. High esterase activities were parallel to high neonicotinoid resistance. CYP6CM1 overexpression was linked to thiamethoxam resistance than to acetamiprid resistance. Both the enhanced esterases and altered target sites were associated with high carbosulfan resistance. This is the first report on the insecticide resistance mechanisms of whiteflies in Sri Lanka. The outcome of the present study can be effectively utilized for a proper whitefly control programme in Sri Lanka, avoiding indiscriminate insecticide usage.

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