Six Years of Successful Management of Whitefly Resistance

Arizona cotton experienced a severe crisis in 1995 stemming from resistance of whiteflies to synergized pyrethroid insecticides. The insect growth regulators (IGRs) Knack® (pyriproxyfen) and Applaud ® (buprofezin) served a pivotal role in resolving this problem. Statewide monitoring of whitefly resistance is conducted annually in Arizona to assess the status of resistance in this important pest. In this paper we provide an update on results from whitefly collections made from 19 cotton fields located throughout Arizona. Overall, whitefly control in Arizona cotton remained excellent in the 2001 season and there were no reported field failures. However, we detected major decreases in susceptibility to Knack of whiteflies collected from cotton. Whereas it was extremely rare to have any whiteflies surviving bioassays of 0.1 µg/ml from 1996 to 1998, this changed in 1999, and by the 2001 season over 60 % of Arizona sites evaluated had •2 % pyriproxyfen-resistant whiteflies. One collection from Eloy, Arizona, in 2000 had>50 % of whiteflies surviving Knack bioassays of 0.1 µg/ml. Whiteflies throughout Arizona continued to be moderately less susceptible to Applaud, relative to susceptibility levels in 1996, when the IGRs were firs