The seasonal storage of dried citrus pulp has created a serious warehouse insect problem because this commodity is very susceptible to insect infestations. The presence of insects not only affects the composition of the dried citrus pulp but also makes it undesirable to shippers, warehousemen, and the consumer because of the danger of spreading the infestation to other commodities in the vicinity. Being an animal feed it must not contain any harmful insecticide residues and, therefore, the insecticides and the methods of applying them on this commodity are limited. The weekly aerosol applications of synergized pyrethrum commonly used for the past several years have been very expensive and not very effective. The problem has been to develop an effective low cost treatment acceptable under Section 406 of the Food, Drug, and Cosmetic Act. Laboratory tests showed that wettable powder formulations produced heavier, longer-lasting, and more toxic surface residues than aerosols containing the same active ingredients. This paper describes the evaluation of the practicability and comparative effectiveness of these findings under field conditions. Thirteen stacks of feed were treated with pyrethrum-piperonyl butoxide: 2 with aerosol formulations and 11 with the wettable powder formulations applied to the surface of the stacks. The insecticide residue obtained with wettable powder was more than 10 times that obtained with the aerosol treatment. Some of the insecticide migrated through the burlap hags, hut the amount was very small in comparison with the amount that accumulated on the stack surface. The use of vinyl stack covers over the feed after two applications of the wettable powder appears very promising. The wettable powder was much more effective in maintaining a low insect population in the feed than the aerosol treatments. The tests also showed that it is practical to use monthly applications of wettable powders at the rate of 5 mg. of pyrethrum and 50 mg-. of piperonyl butoxide per square foot to treat large quantities of stored citrus pulp and that the cost of treatment is less with wettable powders than with aerosols.