Luminal membranes in the midgut of the lace bug Corythucha ciliata.

The inordinately long midgut of hemipterans is devoid of peritrophic membranes described for many other insects. These membranes separate apical microvilli of midgut cells from contents of the lumen. In hemipterans, by contrast, contents of the lumen are separated from apical surfaces of midgut epithelia by secretion of additional plasma membranes (perimicrovillar membranes) containing digestive enzymes. In the lace bug Corythucha ciliata, precursors for these perimicrovillar membranes arise in smooth endoplasmic reticula (SER) as stacked, coiled membranes and are continually expelled into the lumen along the entire length of the midgut as stacked, tubular membranes; these membranes undergo changes in form as they pass from the SER to the midgut lumen. Rather than adopting the double membrane configuration in the gut lumen that was first described for hemipteran perimicrovillar membranes, these modified perimicrovillar membranes of the Corythucha gut line apical surfaces of midgut apical lamellae and intermix with the contents of the lumen; foregut and hindgut epithelial cells are devoid of vesicles containing coiled membranes observed abundantly in midgut epithelia. Rather than achieving renewal of adult midgut epithelial cells through the divisions of regenerative cells as observed in many adult insects, prolific generation of perimicrovillar membranes apparently maintains the integrity of this lengthy hemipteran midgut epithelium.