ULTRASTRUCTURE AND SECRETORY ACTIVITY OF ABRACRIS-FLAVOLINEATA (ORTHOPTERA, ACRIDIDAE) MIDGUTS

The midgut of Abracris flavolineata adults comprises a ventriculus and six anteriorly placed caeca each displaying an anterior and a posteri or lobe, Columnar cells in the caeca and anterior ventriculus present secretory vesicles originating from abundant Golgi areas, which seem t o result (through exocytosis) in dark granules among the microvilli, A . flavolineata males were starved for 24 h, fed for 20 min at noon and dissected at 0, 1, 3 and 5 h after the meal, Enzyme assays were accom plished on crop and caecal contents and in subcellular fractions obtai ned from the isolated anterior caeca. Subcellular fractions putatively containing secretory vesicles were recognized, Digestive enzyme activ ity is usually low (amylase is high) in the secretory vesicles in star ving insects, decreases 1 h after the meal, increases at 3 h, and ther eafter decreases again (amylase remains constant), In caecal contents, digestive enzymes decrease at 1 h and increase at 3 h after the meal, the contrary being true for crop contents, Thus, in A. flavolineata c aecal cells, digestive enzymes (beta-glucosidase is an exception) are synthesized and secreted by exocytosis in response to feeding, Also in response to feeding, digestive enzymes are transferred from caecal co ntents to the crop and, after about 3 h following the meal, crop-caeca l dispersed material with accompanying enzymes are translocated to the caeca, where digestion ends and absorption occurs. (C) 1997 Elsevier Science Ltd.