Efficacy of Certain Neonicotinoids Against Cotton Whitefly, Bemisia tabaci and Their Residues in Fruits and Leaves of Tomato Plants under Open Field Conditions

Abstract

Globally, neonicotinoids constitute a class of systemic insecticides that has become the most widely utilized group of insecticides. The efficiency of three neonicotinoid insecticides i.e. imidacloprid, thiamethoxam and dinotefuran at recommended dose were studied against the cotton whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) on tomato plants under the open field conditions. The results showed that imidacloprid was the most efficient insecticide against the nymphs of B. tabaci followed by thiamethoxam and dinotefuran. The general means of reduction percentages of B. tabaci nymphs were 85.75, 83.24 and 75.11% after the 1 st spray and 87.53, 85.03 and 73.96% after the 2 nd spray for imidacloprid, thiamethoxam and dinotefuran, respectively. Residues of the tested pesticides in/on tomato fruits and leaves were determined using a QuEChERS method. Initial amount of the three insecticides were higher in tomato leaves compared with fruits. The half-life values (t½) for the three insecticides in tomato fruits were 2.71, 2.95 and 1.87 days for imidacloprid, thiamethoxam and dinotefuran, respectively. While these values in tomato leaves were 2.91, 3.322 and 2.108 days for imidacloprid, thiamethoxam and dinotefuran, respectively. The levels of residues were above the maximum residue limits (MRLs) up to 3, 6 and 6 days after spray (DAS) for imidacloprid, thiamethoxam and dinotefuran, respectively in tomato fruits. The determined PHI for imidacloprid, thiamethoxam and dinotefuran were 6, 9 and 9 DAS, respectively. Washing of treated tomato fruits with tap water, 10% sodium bicarbonate, and 10% vinegar for 15 min were reported to be highly effective in reducing the level of the three insecticides. The residues of the three insecticides in tomato fruits pose low health risks to consumers.