Alimentary canal ofSphaerodema rusticum(F.) (Hemiptera: Belostomatidae)

Summary The alimentary canal of Sphaerodema rusticum is nearly four times the body length. The foregut consists of pharynx and oesophagus. The long midgut is differentiated into three regions; the second and third midgut regions shrink in length when starved. Four Malpighian tubules originate individually at the midgut-hindgut junction. The hindgut consists of a tubular ileum and a thin-walled rectum with a saccular, rhythmically contracting rectal caecum. The ileum has a membranous area on its left side. The foregut epithelium is syncytial; the oesophagus invaginates slightly into the midgut. The midgut epithelium is folded, forming many cell nests with the nidi at the bottom of the folds. Unlike the second midgut, the first and third midgut regions show different histological pictures in fed and variously starved conditions. The first and third midgut appear to be secretory and the second midgut absorptive in function. Secretions are of holo-, mero-, and lemmocrine types. A peritrophic membrane was not found in S. rusticum, but the controversy regarding its presence and nature in Hemiptera has been discussed. A well-developed proctodaeal valve, not apparent in gross anatomy, is present at the midgut-hindgut junction. The ileum is composed of both columnar and membraneous epithelia. Rectum and rectal caecum have a membraneous and syncytial epithelium. Glycogen is absorbed and stored in the midgut and hindgut, which becomes exhausted during starvation.