Digestion of legume starch granules by larvae of Zabrotes subfasciatus (Coleoptera: bruchidae) and the induction of alpha-amylases in response to different diets.

Zabrotes subfasciatus larvae possess three alpha-amylase isoforms as determined by in gel assays following SDS-PAGE. The two minor isoforms present lower electrophoretic mobility than the major form, and seem to occur as a heterodimer. When developed inside Vigna unguiculata (cowpea) seeds, fourth instar larvae have minor quantities of the slow-migrating forms, but when reared on seeds of Phaseolus vulgaris (common bean) or Phaseolus lunatus, the two slow-migrating forms are expressed in higher amounts, while activity of the major form was independent of the host seed. Larvae developing inside cowpea seeds at the beginning of the fourth instar were fed on flour from cotyledons of cowpea or common bean. Larvae fed on the common bean flour started to express the dimer in higher amounts when compared with the control larvae fed on cowpea flour. In an attempt to correlate differences between starch granules and the induction of alpha-amylases, a detailed study on the digestive process of the granules was conducted. Incorporation of purified starch granules into artificial diets did not induce the two minor alpha-amylases. The in vitro hydrolysis rates of purified granules and the pattern of dextrins liberated by the different alpha-amylases were similar for the two legume species. The starch granules enter the midgut extensively damaged, which may facilitate the access to the more susceptible parts of the granules to enzymatic attack.

Induction of digestive alpha-amylases in larvae of Zabrotes subfasciatus (Coleoptera: Bruchidae) in response to ingestion of common bean alpha-amylase inhibitor 1.

Zabrotes subfasciatus larvae possess three alpha-amylase isoforms determined by in gel assays following SDS-PAGE. Two minor isoforms present lower electrophoretic mobility than the major form. When developed inside Vigna unguiculata (cowpea) seeds, fourth instar larvae have minor quantities of the slow-migrating isoforms, but when reared on seeds of Phaseolus vulgaris (common bean), the two slow-migrating forms are expressed in higher amounts, whilst the quantity of the major constitutive form is independent of the host bean. Larvae at the beginning of the fourth instar were fed on flour or cotyledons of cowpea and common bean and it was observed that the larvae fed on the common bean expressed the two slow-migrating forms in higher amounts when compared to the control larvae fed on cowpea. In order to investigate the possible correlation between the induction of alpha-amylases and the ingestion of the common bean alpha-amylase inhibitor 1 (alphaAI-1), this inhibitor was incorporated into artificial diet. It was observed that larvae fed on diet containing chronic doses of alphaAI-1 during their development, produced the two slow-migrating forms in higher amounts than control larvae, however, fourth-instar larvae fed on the same diet presented less amylase activity than control larvae. The data suggested that alphaAI-1 is involved in amylase induction and that it has inhibitory activity against the constitutive amylase, when starch granules are used as substrate.