Tolerance to the Seed α-Amylase Inhibitor by the Two Insect Pests of the Common Bean, Zabrotes subfasciatus and Acanthoscelides obtectus(Coleoptera:Bruchidae)

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Abstract
The bean weevil (Acanthoscelides obteclus (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 α-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 α-amylase inhibitor does not suppress the larval growth of Z. subfasciatus. The present investigation examined the mechanism of the tolerance toward the α-amylase inhibitor by A. obtectus and Z. subfasciatus. Comparison of proteolytic changes of the α-amylase inhibitor incubated with larval midgut extracts of C. chinensis, C. maculatus, C. analis, A. obtectus, and Z. subfasciatus showed that the inhibitor was digested only by the larval midgut extract from Z. subfasciatus. The digestion seemed to cause the inactivation of the α-amylase inhibitor protein. On the other hand, the larval midgut extract of A. obtectus had no effect on the α-amylase inhibitor. It is likely that the tolerance mechanism to the α-amylase inhibitor of A. obtectus differed from that of Z. subfasciatus.