Control failure of Sri Lankan whitefly (Bemisia tabaci Genn.) is due to high resistance development against recommended insecticides

Whitefly, Bemisia tabaci Genn. is a major pest of vegetables. Control of the whitefly has become a major problem in agriculture pest control programmes despite the use of several recommended insecticides. No studies have been carried out previously in Sri Lanka to evaluate the insecticide resistance status of B. tabaci. The present study focused on identifying the resistance status of B. tabaci from three main climatic zones of Sri Lanka. Field collected or laboratory reared (up to 5th generation) adults from Gannoruwa (n = 3612), Kahatagasdigiliya (n = 3385) and Bandarawela (n = 4146) were exposed to different concentrations of recommended insecticides, i.e. two neonicotinoids (thiamethoxam and acetamiprid), an organophosphate (profenofos), a carbamate (carbosulfan) and a pyrethroid (etofenprox), using leaf-dip method. Log-probit mortality curves were obtained for each insecticide, and compared with published data available for susceptible populations and the dosages recommended by the Department of Agriculture (DOA) of Sri Lanka. Resistance factors (RF) ranged from 2.74 ‒ 789.48 and the highest resistance was observed for etofenprox. Moderate to high resistance to neonicotinoids and moderate resistance to carbosalfan was evident. All three populations were largely susceptible for profenofos. The populations exhibited significant heterogeneous responses at least for one insecticide except for carbosulfan. A 6 to 800 fold increase of the DOA recommended dosages are needed to gain 90 % mortality of the populations except for profenofos. An integrated approach to manage insecticide resistance guided with a regular resistance monitoring programmes is urgently required for effective control of the whitefly in horticultural crops in Sri Lanka.