Analysis of the ultrastructure and formation pattern of the peritrophic membrane in the cupreous chafer, Anomala cuprea (Coleoptera: Scarabaeidae)

Abstract

The peritrophic membrane (PM) of insects plays several important roles in the midgut. However, the fine structures of the PM that could be associated with these roles have not been studied in detail, especially in the Coleoptera. Here, we examined the ultrastructure of larvae of a major scarabaeid pest of agriculture and forestry nurseries, Anomala cuprea Hope, by electron microscopy. The major type of microvilli that should serve as a template for formation of the meshwork were unexpectedly shorter than those in almost all other insect species presented previously. The presence of newly formed PM in the anterior region of the midgut strongly suggested the PM of this insect is formed at least in the anterior region of the midgut, contrary to those in most other Coleoptera reported, which were formed in the middle or posterior region. Based on Terra’s method, the anterior PM was found to contain chitin. A number of small amounts of assembled food particles were individually enclosed by fragment(s) of chitin-matrix layer(s). The pore size and multi-laminate structure of the inner chitin-matrix layers in the PM suggest that the layers can mostly prevent parasitic entomopoxvirus virions from passing through the inner part of the PM.