Effects of Nosema apis infection on honey bee (Apis mellifera) digestive proteolytic enzyme activity

Activity levels of four bee midgut proteolytic enzymes were measured in adult honey bees 3, 8, and 24 days after dosing with spores of Nosema apis. Trypsin and chymotrypsin activity levels were significantly lower in N. apis-dosed bees than in the controls at each time point. Elastase levels were significantly lower than controls in dosed bees examined at 8 and 24 days, but not at 3 days. Leucine aminopeptidase levels were lower in dosed bees at days 3 and 8, but not at day 24. In both the dosed and the control bees, levels of each of the four enzymes were significantly higher at days 3 and 8 than at day 24. Microscope checks of preparations made from the guts of the bees examined for enzyme activity and from other bees dosed in the same manner, confirmed the efficacy of the dosing procedure, as did a comparison of mortality among dosed and control bees. Reduced digestive proteolytic activity in young bees infected with N. apis may explain why hypopharyngeal gland development is disrupted in these insects. (C) 1998 Academic Press.