Partial biochemical characterization of α- and β-glucosidases of lesser mulberry pyralid, Glyphodes pyloalis Walker (Lep.: Pyralidae)

The Lesser Mulberry Pyralid, Glyphodes pyloalis, is an important pest of mulberry. This pest feeds on mulberry leaves, and causes some problems for the silk industries in the north of Iran. The study of digestive enzymes is highly imperative to identify and apply new pest management technologies. Glucosidases have an important role in the final stages of carbohydrate digestion. Some enzymatic properties of alpha- and beta-glucosidases from midgut and salivary glands of G. pyloalis larvae were determined. The activities of alpha- and beta-glucosidase in the midgut and salivary glands of 5th instar larvae were obtained as 0.195, 1.07, 0.194 and 0.072 micromol(-1) min(-1) mg protein(-1), respectively. Activity of alpha- and beta-glucosidase from whole body of larval stages was also determined. Data showed that the highest activity of alpha- and beta-glucosidase was observed in the 5th larval stage, 0.168 and 0.645 micromol(-1) min(-1) mg protein(-1), respectively and the lowest activity in the 2nd larval stage, 0.042 and 0.164 micromol(-1) min(-1) mg protein(-1), respectively. Results showed that the optimal pH for alpha- and beta-glucosidase activity in midgut and salivary glands were 7.5, 5.5, 8-9 and 8-9 respectively. Also, the optimal temperature for alpha- and beta-glucosidase activity in the midgut was obtained as 45 degrees C. The addition of CaCl(2) (40 mM) decreased midgut beta-glucosidase activity whereas alpha-glucosidase activity was significantly increased at this concentration. The alpha-glucosidase activity, in contrast to beta-glucosidase, was enhanced with increasing in concentration of EDTA. Urea (4 mM) and SDS (8 mM) significantly decreased digestive beta-glucosidase activity. Characterization studies of insect glucosidases are not only of interest for comparative investigations, but also understanding of their function is essential when developing methods of insect control such as the use of enzyme inhibitors and transgenic plants to control insect pest.