EXPRESSION OF POLYHEDRON AND P10 IN THE MIDGUT OF ACMNPV-INFECTED SPODOPTERA-EXIGUA LARVAE - AN IMMUNOELECTRON MICROSCOPIC INVESTIGATION

The replication of Autographa californica nuclear polyhedrosis virus (AcMNPV) in midgut epithelia of second-instar Spodoptera exigua larvae was studied using light and electron microscopy. Immunogold labeling and silver enhancement techniques were employed to localize cytopathic structures at early stages of infection. Polyhedra were detected as early as 30 hr post infection in a few columnar and regenerative cells of the epithelium. Sixty-two hours after infection large numbers of columnar and regenerative cells showed the full complement of cytopathic structures, including polyhedra, fibrillar structures, and electron-dense spacers, as normally seen in AcMNPV-infected fat body and tracheal cells. The polyhedra in the regenerative cells were of a normal size and occluded virus particles. The polyhedra in the columnar cells were relatively small and did not contain occluded virus particles. Infected columnar cells were found rejected into the gut lumen, whereas infected regenerative cells had invaded into the midgut epithelium cell layer. Infected larvae that had molted into third instar showed limited signs of infection; only a few columnar and regenerative cells were affected. Since most of the applied promoters for foreign gene expression are derived from AcMNPV late genes, the consequences of synthesis of AcMNPV late gene products in the midgut of S. exigua are discussed with regard to the design and effectiveness of baculovirases with enhanced insecticidal activity. © 1993 Academic Press. All rights reserved.