Distribution of inhibitors of rice weevil (Coleoptera: Curculionidae) alpha-amylases in milled fractions of hard red winter wheat

α-Amylase inhibitor content of milled fractions of hard red winter wheat was determined by assay against two α-amylase isozymes, RW-1 and RW-2, from the rice weevil, Sitophilus oryzae (L.). Saline extracts prepared from flour (predominantly endosperm) were 9- and 15-fold more inhibitory against RW-1 and RW-2, respectively, than were extracts prepared from bran (bran plus shorts). Milled germ contained relatively little inhibitory activity against either isozyme. Isozyme RW-2 was about 3-fold more sensitive than RW-1 to extracts from each fraction. Electrophoretic analysis indicated no major qualitative differences in inhibitor composition among flour and bran fractions. Although the bran fraction contained significant amounts of inhibitor, bran is generally not ingested by larvae or adults of Sitophilus spp. Ingestion of inhibitors from wheat occurs primarily through consumption of endosperm components.