PASSAGE OF AUTOGRAPHA-CALIFORNICA NUCLEAR POLYHEDROSIS-VIRUS THROUGH THE MIDGUT EPITHELIUM OF SPODOPTERA-EXIGUA LARVAE

A special recombinant of Autographa californica multicapsid nuclear po lyhedrosis virus (AcNPV) was designed to study the early histopatholog ical events of baculovirus infection in Spodoptera exigua larvae. This recombinant contained a Drosophila melanogaster heat shock 70 promote r driving an Escherichia coli beta-galactosidase (Lac-Z) reporter gene to monitor the presence of early viral gene expression and a second r eporter gene, the E. coli beta-glucuronidase (GUS) gene, under control of the very late AcNPV p10 promoter to monitor viral replication. In S. exigua larvae, permissive Spodoptera spp. cultured cells, and nonpe rmissive D. melanogaster cultured cells early viral gene expression wa s indicated by the appearance of Lac-Z as early as 3 hr p.i. Late vira l gene expression was indicated by the appearance of GUS and occurred only in the permissive cultured cells and larvae. Early and late viral gene expression could be detected simultaneously using differential e nzyme histochemistry. Analysis of infected S. exigua larvae revealed t hat midgut columnar cells and, at a low frequency, midgut regenerative cells were the primary sites of infection. Parental nucleocapsids wer e apparently transported through columnar cells to underlaying regener ative cells before virus replication and progeny production. Infection of tissues beside the midgut epithelium was not detected prior to vir al replication within the midgut, suggesting that infection of the mid gut is an important prelude to systemic infection. (C) 1995 Academic P ress, Inc.