CONTROL OF FOREGUT CONTRACTION IN THE BLACK FIELD CRICKET, TELEOGRYLLUS-COMMODUS WALKER (GRYLLIDAE, ORTHOPTERA)

Very little information is available regarding the nervous and/or humoral control of foregut peristalsis associated with feeding in insects. Using the cricket, Teleogryllus commodus Walker, we have examined the effect of feeding and the chemicals, proctolin and 5-hydroxytryptamine (5-HT), on contraction of isolated foreguts. Both diet and the presence of food in the crop influence the pattern of contraction. Proctolin and 5-HT increase contraction in a dose-dependent manner between 1 pmol l(-1) and 1 mu mol l(-1). Comparison of the effects of proctolin (10 nmol l(-1) and 1 mu mol l(-1)) and 5-HT (1 mu mol l(-1)) indicated that 5-HT always had the greatest stimulatory effect. The difference between the two chemicals resulted from stimulation of crop peristalsis by 5-HT. Gut contractions continued to be elevated after replacement of 5-HT by normal saline, although this residual effect was reduced when the ingluvial ganglia were removed. An increase in spontaneous contractile activity of the foregut was observed when the foregut remained connected to the midgut/hindgut. Addition of the isolated midgut to the saline bathing the foregut resulted in changes in the contraction pattern within 10 s. This work indicates that feedback from the midgut and chemicals released either from the central or stomatogastric nervous systems influence foregut contraction.