Observations on the presence of the peritrophic membrane in larval Trichoplusia ni and its role in limiting baculovirus infection.

Light microscopical examinations of dissected and stained peritrophic membranes (PMs) were conducted to determine the presence or absence of this protective structure in larvae of Trichoplusia ni, prior to and through ecdysis. Observations of fourth- and fifth-instar larvae of T. ni from two independent rearing colonies showed that PMs were present and lined the midgut prior to, during, and immediately after ecdysis in both instars. Western blot analysis of insect intestinal mucin (IIM), a major protective protein in the T. ni PM, indicated that synthesis of IIM occurred during T. ni embryonic development, or more precisely, that IIM synthesis started approximately 4 h prior to hatching. These results demonstrated that the neonate T. ni midgut is lined with a protective mucinous layer at hatching. A baculovirus enhancin from T. ni granulosis virus (TnGV) enhanced per os viral infections of budded viruses (BVs) of Autographa californica multiple nuclear polyhedrosis virus (AcMNPV) and T. ni single nuclear polyhedrosis virus (TnSNPV) in neonate, fourth-, and fifth-instar larvae of T. ni. These results provided further evidence that the PM may serve as a partial barrier to viruses in the midgut lumen and that enhancins can facilitate the infection process.