Laboratory tests with field-collected foliage showed the selected strain of Trioxys pallidus was also resistant to Lorsban, Thiodan, Supracide, and Zolone, pesticides used in walnut IPM programs.

This research was supported in part by funds from the Walnut Board of California, W-84, and the California Agricultural Experiment Station. The authors thank Robert Beede, Bill Krueger, Bill Olson, Kevin Spollen, and Gary Obenauf for assistance with the project. They also thank B. Bisabri, Dow Chemical Company, Davis, California, for assistance with the experimental walnut block and spray applications and T. L. Speed, Department of Statistics, University of California, Berkeley, for advice with the statistical analysis.