A rapid bioassay that detects buildup of resistance can help growers avoid the expense and hazard of wasted pesticide treatments.

The authors thank Bonnie Beffa, Steve Lorenzato, and Sherita Normington for technical assistance; Rohm & Haas and Uniroyal Chemical Companies for providing acaricides; and Dellavalle Laboratories for use of their facilities. They are also grateful to the growers and pest control advisors for use of cotton fields. This project was supported in part by funds from the UC/IPM pro gram, CPCSD, Cotton Incorporated, and the Environ mental Monitoring and Pest Management Division of the California Department of Food and Agriculture. The rapid bioassay dishes and testing service are currently available from Insect Lore Products, P.O. Box 1535, Shafter, Ca 93263.