SOME STUDIES ON THE GUT OF VALANGA NIGRICORNIS BURMEISTER (ARTHROPODA, INSECTA)

Abstract

The structure of the gut of Valanga nigricornis resembles that of most acridoids. The foregut is well developed. The midgut is the shortest part of the gut. Twelve groups of Malpighian tubules with excretory ampullae open into the midgut. The foregut has a thick muscular sheath while the thin midgut and caeca have little muscular tissue. The connective tissue is well developed in the hindgut except the colon. The intima is present in the foregut and hindgut. A peritrophic membrane is present in the midgut and hindgut. The foregut is lined internally by squamous or cuboidal epithelium; the caecum, midgut, part of the ileum and the rectal pad, by columnar epithelium while the colon and rectum proper by cuboidal epithelium. In the midgut the zymogen granules are abundant in the basal part of the inner epithelial cells were mitochondria are also most abundant. The cells lining the Malpighian tubules lack zymogen granules. Histochemical tests for carbohydrates, protein and lipid were carried out for different regions of the gut. The following enzymes were found in V. nigricornis, namely amylase, optimal pH 7.0-7.2; alpha-glucosidase, 6.0; beta-glucosidase, 6.0; alpha-galactosidase, 7.0; beta-galactosidase, 6.0; proteinases, 5.8 and 7.8 with casein as substrate, 6.0 with gelatin as substrate; lipase, 8.2. Comparison of the enzymic activities per unit weight of various regions of the gut showed that the midgut tissue was the most potent. The midgut fluid and the foregut fluid contained approximately similar amount of enzymes. When the enzymic activities of the various parts of the gut were compared, the caecum showed as much activities as the midgut. The hindgut fluid and hindgut tissue were the least active. Each enzyme showed different KM values for different substrates. Different optimal pH resulted in different KM values for the same substrate of proteinases. Beta-galactosidase was not inhibited by high temperature, (60°C) treatment. To destroy half of the activity in the crude extract of each enzyme at its optimal pH the period of treatment for each of the following enzymes are: 931 minutes for amylase, 29 minutes for alpha-glucosidase, 58 minutes for beta-glucosidase, 188 minutes for alpha-galactosidase, 105 minutes with gelatin as substrate, 38-39 minutes with casein as substrate for proteinases and 162 minutes for lipase. The approximate digestibility of different plant food varied. It ranged from 28 to 76%. There was no difference in the approximate digestibility between males and females except in one case and there was no apparent decline in approximate in approximate digestibility from nymphs to adults. Valanga showed a definite preference for certain plan species as food and all the favoured species are cultivated plants.