Modified Maximum Dose Bioassay for Assessing Insecticide Response in Field Populations of Bemisia tabaci (Hemiptera: Aleyrodidae)1

The sweetpotato whitefly, Bemisia tabaci (Gennadius) MEAM1 (Hemiptera: Aleyrodidae), continues to be a major pest of vegetable cultivation in Georgia, USA. Field-by-field surveying is an effective approach to determining the susceptibility status of a B. tabaci population to an insecticide. During 2020–2022, a modified maximum dose bioassay method was tested to characterize the insecticide response of B. tabaci field populations to several commonly used insecticides for whitefly management in Tift Co., GA, and the surrounding areas. A rapid bioassay was used for these evaluations that allowed for field assessments before spray applications to reduce the adult life stage of this species. The results of the evaluations were produced within 24-h following a 24-h root drench period. Our survey suggests that the neonicotinoids dinotefuran and flupyradifurone were the most effective insecticides from the Insecticide Resistance Action Committee (IRAC) group 4A. Cyantraniliprole was also effective, with 88 and 86% adult mortality following exposure to the high (maximum) and low doses, respectively. Conversely, the levels of control using another diamide, cyclaniliprole, were notably lower. Adding a low dose to the high dose provided an early indication of inefficient control with a product potentially indicating an increase in resistance. Specifically, a significant difference between the high and low doses suggests that the dose–response curve had shifted toward resistance development in each B. tabaci field population. The proposed bioassay method is meant for systemic insecticides that offer quick responses on adults. The use of this efficient method will improve evaluations prioritizing insecticides for use or rotation in an insecticide resistance management program.