The effects on animals feeding on resistant plants of widespread use of herbicides were studied. Aphids of the speciesSipha (Rungsia) maydisPasserini (Chaitophoridae) andSchizaphis graminumRondani (Aphididae), which feed on phloem sap of corn(Zea maysL.), were used as test‐organisms. Atrazine, an herbicide that acts via root absorption, is toxic to aphids, and this effect is manifest rather rapidly. In both aphid species was found rather severe tissue damage, which could be responsible for the death of animals. The most striking damage occurred in the digestive apparatus.