Uptake and Retention of Imidacloprid and Cyantraniliprole in Cotton for the Control of Bemisia tabaci (Hemiptera: Aleyrodidae)1

Plant tissue bioassays are a standard approach for bioassaying insects such as the sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), an insect that specializes in systemic feeding on the phloem in leaves by using a piercing-sucking mouthpart apparatus. Systemic insecticides remain the most effective approach to whitefly management; however, little work has been done to quantify the amount of insecticide active ingredient that a species is exposed to when feeding. This study was conducted to estimate the imidacloprid and cyantraniliprole concentrations present in cotton (Gossypium hirsutum L.) leaves 24 h after a root drench for systemic toxicological bioassays. Insecticide active-ingredient quantification involved liquid chromatography–tandem mass spectrometry. Comparable concentration responses also were conducted to indicate the mortality of the sweetpotato whitefly at the tested concentrations. The results indicated significant active-ingredient retention with higher concentrations of insecticide treatments, which corresponded with higher sweetpotato whitefly mortality. Specifically, for imidacloprid and cyantraniliprole, the average slopes and intercepts of the log parts per billion of leaf tissue concentration to milligrams of active ingredient per liter of treatment solution were y = 4.08 x + 0.83 and y = 6.22 x + 0.47, respectively. These formulae estimate leaf tissue concentrations that can be linked to insect insecticide exposure in the leaves, with 50–73% of the overall variability explained. Significant correlations also were observed between the root drench concentrations, leaf tissue concentrations, and sweetpotato whitefly mortality.