Structure and formation of the peritrophic membrane in the larva of the southern corn rootworm, Diabrotica undecimpunctata

The peritrophic membrane (PM) in larvae of the southern corn rootworm Diabrotica undecimpunctata (Coleoptera:Chrysomelidae) forms along the full length of the midgut epithelium, defining D. undecimpunctata as a Type I insect with respect to PM formation. PM formation occurs in three phases: organization of a continuous lamella of matrix from material secreted into the interstices between the microvilli, maturation and apical movement of the lamella along the microvilli, and shedding of the lamella from the tips of the microvilli into the midgut lumen. Subsequent cycles of synthesis and shedding give rise to multiple, concentric lamellae which surround the food in the gut lumen. PM lamellae are 0.2 mum in profile width and consist of a core of bundles of 5 nm-diameter microfibers encased in a finely-granular homogeneous material. The microfiber bundles are arranged in an orthogonal grid-like array with dimensions consistent with formation around the microvilli. The homogeneous material separates from the PM lamellae to enclose food particles suggesting it may contain digestive enzymes. The PM, microvilli and intracellular vesicles in the midgut epithelium stain intensely with wheat germ agglutinin reflecting the presence and sites of secretion and synthesis of chitin.