The importance of natural biotype differences affecting insect pest status and consequent pest management is indicated and discussed, including the occurrence of such differences in association with resistance to pesticides. Data on observed differences, especially those affecting the capacity to damage stored grain, are presented forRhyzopertha dominica, Prostephanus truncatus, Sitophilus oryzaeandTribolium castaneum.Simple tests to discriminate between biotypes, in this capacity and in some other characteristics, are briefly described. It is proposed that such tests should be included where pest management improvements are a research objective, and that their potential usefulness in field situations, where the information obtained may be especially relevant, should be more widely considered.