In recent yrs. various investigators have found that certain external parasites on both animals and plants can be controlled by feeding the host organism chemicals toxic to the parasites. For example, 100% mortality of bedbugs was obtained when they were allowed to feed on a rabbit 3-5 hours after DDT was administered to the host in doses of 228-400 mg. per kg. of body wt. In like manner, apple grain aphids and red spiders on wheat plants have been eliminated by adding 3 ppm. of Se to the nutrient soln. in which the plants were grown. Inasmuch as it seems now that compounds highly insoluble in water are no longer eliminated from such usage in both plants and animals, these findings open up a field of research that promises to yield results of great value.