Age-related changes in midgut ultrastructure and trypsin activity in the honey bee, Apis mellifera

Abstract

— Trypsin-like activity was detected in the epithelial tissue, in the fluid of the ectoperitro-phic space, and within the endoperitrophic space of the midgut of adult worker honey bees, Apis mellifera. It was highest in free-flying bees and in caged bees fed pollen. Lower levels occurred in caged bees restricted to sucrose syrup or fed sucrose syrup in addition to either Beltsville Bee Diet or egg albumin. Levels of midgut trypsin activity were dependent on the amount of protein diet consumed. Both diet consumption and trypsin-like activity decreased as the bees aged. Ultrastructu-ral changes in the midgut tissue accompanied this decline in enzymatic activity. In five-day-old pollen feeding bees, the apical cytoplasm of cells in the posterior midgut contained numerous electron-opaque vesicles, and the brush border in the crypts of the distal midgut was composed of short pleomorphic microvilli. Apical discharge from the midgut cells released the opaque vesicles into the midgut lumen. However, in 30-day-old field bees, the number of opaque vesicles and the microvesi-culation of the brush border were reduced. Thus, the presence of the endogenously produced endo-protease and the regional variation in cell ultrastructure suggest that the honey bee may rely on countercurrent flow to distribute enzymes and nutrients efficiently throughout the midgut. Apis mellifera— midgut ultrastructure-enzymatic activity-trypsin-age