Status of Whitefly Resistance to Insecticides in Arizona Cotton

Abstract

We summarize a whitefly resistance crisis that culminated in 1995 in Arizona cotton and that prompted the development of an integrated resistance management strategy. The strategy incorporated two new major elements: once-per-year use of the insect growth regulators (IGRs), Knack® (pyriproxyfen) and Applaud® (buprofezin), and measures to delay use of pyrethroids for as long into the growing season as possible. A three-stage chemical use recommendation was formulated comprising IGRs (Stage I), other non-pyrethroid insecticides (Stage II), and synergized pyrethroid insecticides (Stage III). Results from use of the strategy in the 1996 season were very promising. Insecticide use for control of whiteflies was reduced substantially where IGRs were used. Statewide monitoring of whitefly susceptibility to key insecticides revealed significant reductions in resistance to synergized pyrethroids as well as to non-pyrethroid insecticides. Resistance to Danitol® + Orthene® was shown to decline sharply from the end of the 1995 season to early in the 1996 season at the Maricopa Agricultural Center. Use of Stage I materials (Knack® and Applaud®) and specific Stage II (non-pyrethroid) insecticides in 1996 resulted in only small reductions in susceptibility to synergized pyrethroids. However, one application of Danitol® + Orthene® yielded a large increase in resistance. These findings confirmed the value of the newly formulated resistance management strategy and indicated that resistance to the synergized pyrethroids can be managed if these insecticides are used sparingly. Additionally, evidence was obtained of collateral resistance buildup and decline in lygus bugs and whiteflies. Substantially reduced susceptibility of lygus bugs was documented in 1995, relative to 1994, coinciding with elevated insecticide use to control resistant whiteflies. Implementation of the 1996 whitefly resistance management program was correlated with increased lygus bug susceptiblity to the insecticides Orthene® and Capture® at most locations monitored throughout Arizona.