DIGESTIVE AND ABSORPTIVE SITES ALONG THE MIDGUT OF THE COTTON SEED SUCKER BUG DYSDERCUS-PERUVIANUS (HEMIPTERA, PYRRHOCORIDAE)

The midgut of Dysdercus peruvianus is divided into three sections (V-1 -V-3), which are linked through V-4 to the hindgut. The midgut content s are reducing with a pH around 5.8. D. peruvianus saliva lacks digest ive enzymes and apparently is used only to suspend seed material which is ingested, distending V-1. Most midgut carbohydrase activities are found in V-1, where is also observed a alpha-mannosidase and an aminop eptidase derived from the meal. The high glycosidase and low amylase a ctivities found in V-1 are in agreement with the major and minor cotto n seed content of saccharides and starch, respectively. Water and gluc ose absorption occur without dietary salt ions in V-1. About 5h after the filling of V-1, V-2 is also filled. At V-2, a cysteine-proteinase (pH optimum 5.5, M(r) 53,000) predominates and amino acids are absorbe d. This absorption is activated by potassium and inhibited by sodium i ons. Both midgut alpha-glucosidase and cysteine proteinase activities increase on feeding. As soon as V-1 empties, V-3 is filled. After a lo ng stay (70-90h) in V-2 and V-3, the food passes quickly through V-4 i nto the hindgut. The results on D. peruvianus (Hemiptera: Pentatomomor pha) and literature data on Rhodnius prolixus (Hemiptera: Cimicomorpha ) are used to infer the digestive physiology characteristics of the He teroptera ancestor, and to discuss the major adaptations which occurre d when the bugs moved from a sap sucking habit into a habit which incl uded digestion of polymers.