Insect growth regulators (IGRs) served a critical role in overcoming the whitefly resistance crisis that occurred in Arizona in 1995. With the granting of a section 18 exemption in 1996, an integrated resistance management strategy was implemented to sustain the efficacy of the IGRs by using them sparingly and in the context of IPM. Bioassay methods were adapted to test susceptibility of Arizona whitefly populations to the growth regulators buprofezin (Applaud^®) and pyriproxyfen (Knack^®). Susceptibility of six populations was estimated early in the 1996 season prior to use of IGRs and late in the season after IGR treatments were applied to cotton. All Arizona populations were more susceptible to Applaud and Knack than were Israel whiteflies, based on published reports of Israeli findings. Significant differences were found between Arizona whitefly populations in susceptibility to Applaud and Knack during both the early and late season evaluations. Probit responses of the bulked data for all six populations early and late-season were indistinguishable for response to Applaud but significantly higher for late-season response to Knack. Field performance of both IGRs was excellent. Knack provided a minimum of 30 days whitefly suppression, while Applaud provided at least 14 days suppression. The numbers of insecticide treatments applied for whiteflies was reduced greatly in 1996, relative to 1995. Findings from the Netherlands and Israel have demonstrated the relatively rapid development of whitefly resistance to both Applaud and Knack. To sustain the impressive turn-around in whitefly control achieved with the IGRs, we recommend that Arizona cotton growers continue to limit the use to once per season, while strongly emphasizing delaying use of pyrethroids, conservation of natural enemies, and appropriate use of monitoring and thresholds.