Digestion in larvae of Callosobruchus maculatus and Zabrotes subfasciatus (Coleoptera : Bruchidae) with emphasis on alpha-amylases and oligosaccharidases

Determinations of carbohydrases, aminopeptidases and acid phosphatase in th e larval midgut cells and in the luminal contents of Callosobruchus maculat us and Zabrotes subfasciatus have been carried out. The results showed that larvae of both species displayed similar distribution of digestive enzymes in the intestinal compartments. Most larval digestive enzyme activities we re found in the luminal contents. Of the activities found in the midgut tis sue, only aminopeptidase is predominant in the membrane fraction. Compariso ns of activities recovered from a seed flour mass equivalent to the midgut mass showed that a high percentage of the luminal aminopeptidase activity a nd, to a lesser extent, alpha-galactosidase activity, can be derived from t he seeds, whereas the other enzymes are produced by the insects. Activities against starch, maltose and maltodextrins were found to show the highest l evels of activity, followed by enzymes active against galactosyl oligosacch arides. Based on differences in elution profiles on hydrophobic chromatogra phy and banding patterns in mildly denaturing electrophoresis, both species showed a multiplicity of glycosidases. The data suggest that the majority of carbohydrate digestion occurs in the midgut lumen, whereas protein diges tion should take place partly in the lumen and partly at the cell surface. Larvae of Z. subfasciatus can modulate the levels of alpha-amylases and alp ha-glucosidase in response to different diets. The complex of carbohydrases found is qualitatively appropriate to digest the free oligosaccharides and oligomaltodextrins produced by alpha-amylases from the starch granules of host seeds. (C) 1999 Elsevier Science Ltd. All rights reserved.