Activity, release and flow of digestive enzymes in the cricket, Gryllus bimaculatus

Abstract.  In the cricket Gryllus bimaculatus , proventricular pressure forces a nutrient fluid from the ground food-brei through a sieve at the base of the caecae, and the combination of secreted enzymes and water causes a rapid inflation of the caecae on the first day after imaginal ecdysis. The ceacal region of the midgut is the primary site for the secretion of digestive enzymes. Proteases and amylase flow from the caecae into the mostly empty crop on day 1, and carbohydrate and protein digestion starts as soon as food is present (6 h). Thereafter, much of the amylase activity (but not protease) in the crop is synthesized and released by the crop tissues themselves. Regurgitating proteases and amylases from the caecae into the crop after day 1 is most likely accomplished by temporarily halting proventricular peristalsis and allowing the caecal muscles to contract, forcing caecal contents, including enzymes, forward. The total activity of digestive enzymes in the caecae is virtually identical in 2-day-old fed and unfed females, indicating little or no secretagogue (prandial) regulation of enzyme secretion. Most of the digestive enzymes in the ventricular endoperitrophic space may originate from the mucus dragged from the caecae. Lipase activity is low in all gut regions in both starved and fed females. Head ligation or injection of trypsin modulating oostatic factor, allatostatin A or B fails to indicate any involvement of nerves or hormones in the release of digestive enzymes in the caecae. Gryllus bimaculatus appears to secrete digestive enzymes continuously, and a considerable loss of enzymes may occur at certain times through egestion.