Histopathology of cytoplasmic polyhedrosis virus (Reoviridae) infection in corn earworm, Helicoverpa zea (Boddie), larvae (Insecta: Lepidoptera: Noctuidae)

Abstract

Histopathology of cytoplasmic polyhedrosis virus (CPV) infection in the larval midgut of the corn earworm, Helicoverpa (=Heliothis) zea (Boddie) is described. Small polyhedral inclusion bodies (PIB) are observed in columnar cells of the midgut 1 or 2 days after treatment with CPV. Virions are partially or completely occluded in a polyhedral matrix to form PIB at the periphery of the virogenic stroma. PIB are dodecahedral in shape with a hexagonal outline and measure from less than 1 to 4 μm in size. Virions measure about 50 nm in diameter. Microvilli of infected columnar cells are not affected until immediately prior to rupture of the cell. Some infected columnar cells ruptured to release PIB into the gut lumen 2 or 3 days after infection. PIB are also released into the lumen by extrusion of heavily infected columnar cells. Mitochondria and rough endoplasmic reticulum deteriorate as infection progresses, and in many cells with advanced infection, the nucleus is obscured. PIB are found in goblet cells 5 days after infection. Infected goblet cells degenerate to such an extent that only a few of the original microvillus-like cytoplasmic projections and cell organelles are left. The implications of CPV infection in integrated pest management of the corn earworm are discussed.