THE EFFECT OF DIETARY PLANT GLYCOSIDES ON LARVAL MIDGUT BETA-GLUCOSIDASES FROM SPODOPTERA-FRUGIPERDA AND DIATRAEA-SACCHARALIS

Spodoptera frugiperda development and midgut beta-glucosidase activity are not affected by salicin and amygdalin present in their diets up t o a concentration of at least 0.5%, suggesting that glycoside toleranc e results from aglycone detoxification. Both salicin and amygdalin aff ect Diatraea saccharalis development, whereas only 0.5% amygdalin caus es a decrease in midgut beta-glucosidase activity. There are three ele ctrophoretically-resolved beta-glucosidases in D. saccharalis midguts. beta-Glucosidases 1 and 3 are thought to hydrolyze amygdalin to gluco se and prunasin, and beta-glucosidase 2 to hydrolyze prunasin to gluco se and the cyanogenic mandelonitrile. A short (48-h) exposure to 0.5% amygdalin causes a decrease of beta-glucosidase 1 and 3, whereas a lon g exposure (whole larval stage) depresses beta-glucosidase 2 activity. This suggests that glycoside tolerance may result from reduction in t he midgut aryl beta-glucosidase activity without affecting the glycosy l beta-glucosidase activity, which hydrolyzes cellobiose and other bet a-glycans. (C) 1997 Elsevier Science Ltd.