Occurrence of midgut perimicrovillar membranes in paraneopteran insect orders with comments on their function and evolutionary significance.

Hemipterans are characterized by the absence of the peritrophic membrane, an anatomical structure that envelopes the food bolus in the majority of insects. However, the microvillar membranes of many hemipteran midgut cells are not in direct contact with the food bolus, due to the existence of the so-called perimicrovillar membrane (PMM), which covers the microvilli extending into the gut lumen with dead ends. alpha-Glucosidase is a biochemical marker for PMM in the seed sucker bug Dysdercus peruvianus (Heteroptera: Pyrrhocoridae). In this article, we report that adults of the major hemipteran infra-orders (Sternorrhyncha, Auchenorrhyncha, and Heteroptera) have PMM and a major membrane bound alpha-glucosidase, which has properties similar to those of the D. peruvianus enzyme. A polyclonal antibody raised against the enzyme of D. peruvianus recognized the enzymes present in PMM from the above-mentioned hemipteran groups. The same antibody was also able of recognizing perimicrovillar alpha-glucosidase from thrips. No PMM nor membrane-bound alpha-glucosidase were found in Psocoptera and Phthiraptera midguts. This suggests that PMM and PMM-bound-alpha-glucosidase are widespread among insects of the order Hemiptera and of the sister order Thysanoptera. The data support the hypothesis that PMM may have originated in the Condylognatha (Paraneopteran taxon including Hemiptera and Thysanoptera) ancestral stock and are associated with plant sap feeding.