TOLERANCE TO THE SEED ALPHA-AMYLASE INHIBITOR BY THE 2 INSECT PESTS OF THE COMMON BEAN, ZABROTES-SUBFASCIATUS AND ACANTHOSCELIDES-OBTECTUS (COLEOPTERA, BRUCHIDAE)

The bean weevil (Acanthscelides obtectus (SAY)) and the Mexican bean weevil (Zabrotes subfasciatus (BOH.)) cause a serious post-harvest loss of the common bean (Phaseolus vulgaris L.). The seeds of P. vulgaris contain a proteinous alpha-amylase inhibitor, which has been shown to inhibit the midgut amylase activity of larvae of the adzuki bean weevil (Callosobruchus chinensis L.) and the cowpea weevil (C. maculatus F.) and to suppress the larval growth of the two bruchids. The alpha-amylase inhibitor does not suppress the larval growth of Z. subfasciatus. The present investigation examined the mechanism of thc tolerance toward the alpha-amylase inhibitor by A. obtectus and Z. subfasciatus. Comparison of proteolytic changes of the alpha-amylase inhibitor incubated with larval midgut extracts of C. chinensis, C. maculatus, C. analis, A. obtectus, and Z. subfasciatus showed that thc inhibitor was digested only by the larval midgut extract from Z. subfasciatus. The digestion seemed to cause the inactivation of thc alpha-amylase inhibitor protein. On the other hand, the larval midgut extract of A. obtectus had no effect on the alpha-amylase inhibitor. It is likely that the tolerance mechanism to the alpha-amylase inhibitor of A. obtectus differed from that of Z. subfasciatus.