Ultrastructure of the filter chamber complex in the alimentary canal of Eurymela distincta signoret (homoptera, eurymelidae)

Abstract

The detailed morphology and ultrastructure of the filter chamber of Eurymela distincta (Homoptera), a phloem-feeder, is described for the first time. It consists of a close union of anterior and posterior midguts, 3 malpighian ducts and proximal ileum. Three cell-types compose the anterior midgut and their ultrastructures suggest that the primary functions here are storage excretion and production of a surface coat of acid mucopolysaccharide which may bind ions (principal cells), active transport, possibly ion secretion (transitional cells), and passive transport (filter chamber proper cells). The ultrastructures of the 3 cell-types of the posterior midgut are suggestive of an ion-secretory function (large cuboidal cells, and transitional cells of the pylorus), while the filter chamber proper cells are like those in the anterior midgut. The internal malpighian tubule is of 1 cell-type and functions in passive diffusion and active transport, possibly ion-secretion from the haemolymph. The single cell-type of the internal ileum may encourage active water absorption from its lumen across the lateral cell membranes. Proximity of axons containing neurosecretion indicates hormonal control of this water movement. The sheath is 1 cell-type, and surrounds the musculature, tracheoles, and nerves supplying the different parts. The internal oesophagus is of 1 cell-type, and resembles the internal ileum in ultrastructure and possibly in function. The posterior midgut is unlike that of xylem-feeding members of the Auchenorrhyncha in that it is shorter, of greater diameter, is of 2 cell-types, and exhibits an anteriorad migration of the malpighian tubule junction from the primitive hemipteran position. The hypotheses are advanced that these features of the posterior midgut are, in Auchenorrhyncha, characteristic of phloem-feeders and produce, as in mesophyll-feeders, a simple type of filter chamber, while the filter chamber. of xylem-feeders is more complex.