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

Determinations of carbohydrases, aminopeptidases and acid phosphatase in the larval midgut cells and in the luminal contents of Callosobruchus maculatus 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 were found in the luminal contents. Of the activities found in the midgut tissue, only aminopeptidase is predominant in the membrane fraction. Comparisons of activities recovered from a seed flour mass equivalent to the midgut mass showed that a high percentage of the luminal aminopeptidase activity and, to a lesser extent, alpha-galactosidase activity, can be derived from the seeds, whereas the other enzymes are produced by the insects. Activities against starch, maltose and maltodextrins were found to show the highest levels of activity, followed by enzymes active against galactosyl oligosaccharides. Based on differences in elution profiles on hydrophobic chromatography 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 digestion 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 alpha-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.