Environmental control of trypsin secretion in the midgut of the two-spotted field cricket, Gryllus bimaculatus

Abstract The two most important environmental factors controlling the release of trypsin in Gryllus bimaculatus are temperature and food consumption. Food consumption is in turn controlled by food availability (quantity), food quality (contained nutrients, inhibitors), developmental stage, age, sex and the daily light–dark cycle. The secretion of trypsin was higher at an acclimation temperature (AT) of 22 °C than at 32 °C, although the weight of caecal tissue and body weight were lower. The trypsin secretion at both experimental temperatures (25 °C and 35 °C) was almost 2 times greater in crickets maintained at 22 °C AT since egg hatch than those maintained only since the last larval stage, but not at 32 °C AT. Acclimation became increasingly rotational with increased exposure time at different rearing temperatures. The more food consumed the higher the trypsin secretion. Secretion was highest on day 3 in adult females and day 2 in males, corresponding to the day of maximal food consumption. Secretion was less than 20% in starved or cellulose fed females compared to those fed a control diet. Food reached the caeca in starved crickets within 30 min and induced an increased trypsin secretion. Crickets started feeding at the onset of darkness, and trypsin secretion was significantly elevated near the end of the scotophase. The in vivo response to 0.4% soybean trypsin inhibitor (SBTI) fed throughout the last larval stage resulted in reduced growth and a 50% decrease in trypsin secretion in 2 day old adult females. An adaptation to the reduction of trypsin secretion occurred when G. bimaculatus was fed 0.1% and 0.2% SBTI, but not when fed with 0.4%.