Lepidopteran peritrophic membranes and effects of dietary wheat germ agglutinin on their formation and structure

Peritrophic membrane (PM) structure and the effects of dietary wheat germ a gglutinin (WGA) on PM formation were studied in larvae of the European corn borer (ECB), Ostrinia nubilalis, and the tobacco hornworm (THW), Manduca s exta. Growth of ECB was strongly inhibited by low amounts of WGA in the die t (0.05%), whereas THW was not affected by amounts of up to 2%. In ECB larv ae, chitin microfibrils were secreted to form an orthogonal network within the apical region of the anterior midgut microvilli. The network then moved to the tips of the microvilli where proteinacious matrix was added prior t o delamination of a single PM into the lumen to enclose the food bolus. Mul tiple PMs rapidly appeared as the food moved posteriorly and some of these became greatly thickened in the middle and posterior regions of the midgut. WGA in the diet caused hypersecretion of unorganized PM in the anterior mi dgut lumen, disintegration of microvilli, and cessation of feeding. It was also shown to bind to both the chitinous network and to several PM proteins , perhaps causing voids in the PM and sparse matrix material. This allowed the passage of food particles through a defective PM into the ectoperitroph ic space and penetration into the microvillar brush border. Stimulation of PM secretion and cessation of feeding may have been ah response to damage t o the brush border. Unlike ECE, the chitinous network of THW is a randomly organized felt-like structure embedded in a proteinaceous matrix. This PM i s secreted as a thin multilayered structure in the anterior region of the m idgut but multiple and thickened PMs occur in the middle and posterior lume ns of the midgut. THW tolerated high amounts of WGA in its diet with no dis ruption of PM formation or inhibition of growth. WGA did accumulate as larg e masses embedded in the PM, but caused no voids that would allow the penet ration of food particles and subsequent damage to the brush border. Therefo re, differences in PM formation and structure between ECB and THW appeared to affect how WGA interacts with chitinous and proteinaceous components of the PM and subsequent effects on larval feeding and growth. (C) 2001 Wiley- Liss, Inc.