EFFECT OF WHEAT-GERM-AGGLUTININ ON FORMATION AND STRUCTURE OF THE PERITROPHIC MEMBRANE IN EUROPEAN CORN-BORER (OSTRINIA-NUBILALIS) LARVAE

European corn borer (ECB; Ostrinia nubilalis (Hubner)) larvae (third i nstar) fed 0.05% w/w wheat germ agglutinin (WGA) in their diet for 72 h showed very little increase in body weight, whereas weight of contro l larvae increased nearly fourfold. Light and transmission electron mi croscopy studies showed that the morphology of the peritrophic membran e (PM) changed within 24 h after ECB larvae fed on the WGA diet. Where as the PM in the anterior region of the midgut was a thin membranous s tructure in control larvae, the WGA-fed larvae secreted a multiple-lay ered and unorganized PM that contained embedded food particles, bacter ia, and pieces of disintegrated microvilli. Gold-labeled WGA was local ized specifically in the PM and microvilli. The PM of WGA-fed larvae w as inundated with dark-staining amorphous structures that, when incuba ted with anti-WGA, showed heavy WGA localization. The antibody label i ndicated that most of the ingested WGA was found in the PM, with lesse r amounts an the microvillar surface and the least amount within the e pithelium. After 72 h, the middle portion of the mesenteron revealed a thin, compact PM in the control larvae, whereas the PM of the WGA-fed larvae was multilayered and discontinuous, which allowed plant cell-w all fragments to penetrate into the microvilli of the epithelium. Scan ning electron microscopy of PMs from fifth instar ECB larvae fed the W GA diet revealed a breakdown in the chitinous meshwork by 48 h after i nitiation of feeding. The endo-PM surface from control larvae was smoo th and intact, whereas the PM of WGA-fed larvae showed disintegration of the meshwork and a reduced proteinaceous matrix, This allowed bacte ria and food particles to penetrate through the PM into the ectoperitr ophic space and directly contact the microvilli. Therefore, WGA, a pro tein inhibitor of larval growth, interferes with the formation and int egrity of the PM, which exposes the brush border to ingested material. This, in turn, appears to stimulate secretion of additional PM layers , the concomitant disintegration of the microvilli, and cessation of f eeding.