This paper discusses the present distribution of the pink boll worm ( Pectinophora gossypiella Saund.) in Mexico and the southwestern part of the United States, and the intensity of the infestation in each area as revealed by the mechanical inspection of gin trash. The effect of low winter temperatures in a large part of the infested area on control of the insect is mentioned. It summarizes the efforts made to eradicate the rather heavy infestation discovered in the eastern end of the Salt River Valley of Arizona in the fall of 1929, by means of cleanup operations, a non-cotton zone, and delayed planting dates in the restricted zone, and details some of the difficulties encountered due to the subtropical climate of that area. The results of these efforts are reviewed, and the program for the 1931 campaign is outlined. This provides for winter cleaning, plowing, and irrigation of all cotton fields within approximately three miles of infestation, the prevention of growing volunteer cotton, and the delaying of planting until the peak of moth emergence has passed. Mention is also made of the scouting done in Mexico in cooperation with the Mexican Department of Agriculture, to determine the distribution of the pink boll worm on cotton and wild host plants.