Efficacy of bifenthrin against pyrethroid-resistant and -susceptible populations of glasshouse whitefly in bioassays and using three spray application methods

Abstract

Bioassays were performed using uniformly-sized drops to reflect exposure of pyrethroid-resistant and -susceptible populations of Trialeurodes vaporariorum Westwood to ultra-low-volume (ULV) spray deposits of bifenthrin. These assays provided good estimates of the optimum concentration of bifenthrin required to control each population when plots of whitefly-infested poinsettias were treated with ULV charged and uncharged sprays. In some assays the Ohio population was > 100 times more resistant to bifenthrin than the susceptible whitefly strain. Conventional high-volume (HV) spraying was as effective as both charged and uncharged ULV sprays against the resistant population, but none of the methods resulted in acceptable control at the maximum label rate. The charged spray was significantly more effective at controlling the susceptible strain than the other methods, causing 98% mortality at approximately one-half the minimum recommended rate. Although bifenthrin has been used on ornamentals in Ohio for only 2 years, there is already evidence that this pyrethroid is no longer effective against a local whitefly population. The bioassays and spray studies described here demonstrate that this lack of effect is attributable to resistance and not to poor application or ‘field failure’.