EVALUATION OF INSECTICIDE ROTATIONS AND MIXTURES AS RESISTANCE MANAGEMENT STRATEGIES FOR BEMISIA-ARGENTIFOLII (HOMOPTERA, ALEYRODIDAE)

A field population of Bemisia argentifolii Bellows & Perring was subje cted to selective pressure with 5 insecticide regimens: continuous app lications of bifenthrin, endosulfan, chlorpyrifos; bifenthrin-endosulf an-chlorpyrifos rotation and a 1:2 bifenthrin + endosulfan mixture. In secticide resistance developed at variable rates in all whitefly popul ations under selection during this study. Selection with bifenthrin re sulted in early resistance development that steadily increased under c ontinuous selection to 752-fold by generation F-27. With chlorpyrifos and endosulfan selection treatments, low levels of resistance develope d in generations F-7 and F-15, respectively (resistance ratios of 8-fo ld). Resistance development in the rotation and mixture regimens was d elayed for an additional 10 generations. The magnitude of resistance r anged from a high of 752-fold for the single continuous use of bifenth rin to a low of 16-fold resistance for the bifenthrin-endosulfan-chlor pyrifos rotation. The level of resistance was also low under selection by the bifenthrin + endosulfan mixture after 23 generations (resistan ce ratio = 17-fold). Compared with single, continuous insecticide sele ctions in the greenhouse, the rate of resistance development was signi ficantly reduced by rotations and mixtures of insecticides. For all in secticide-selection regimens, slopes of regression lines increased ove r many generations. The whitefly population treated with the bifenthri n + endosulfan mixture generated the steepest lines.