Histologic lesions of experimental infection with Lymantria dispar multicapsid nucleopolyhedrovirus and Lymantria dispar cytoplasmic polyhedrosis virus in European gypsy moth caterpillars (Lymantria dispar dispar)

Abstract

European gypsy moths ( Lymantria dispar dispar) are an invasive species in North America, and are listed by the International Union for the Conservation of Nature as one of the 100 most destructive invasive species worldwide. They have several known viruses, some of which are used as biological control agents. However, there are no detailed descriptions of many entomopathogenic viral infections, including in European gypsy moths, using bright-field microscopy. In this study, 11 European gypsy moth caterpillars were evaluated histologically: 4 were experimentally infected with Lymantria dispar multicapsid nucleopolyhedrovirus (LdMNPV; Baculoviridae); 4 were experimentally infected with Lymantria dispar cytoplasmic polyhedrosis virus (LdCPV; Reoviridae); 3 control animals were uninfected. A complete tissue set was evaluated in all animals from all groups using bright-field microscopy, including epidermis, cuticle, striated muscle, tracheae, foregut, midgut, hindgut, Malpighian tubules, hemocytes, fat body, and nervous system. LdMNPV-infected caterpillars had marked karyomegaly and intranuclear viral inclusions in cells of the epidermis, tracheae, fat body, and hemocytes. LdMNPV-infected caterpillars also had hyperplasia and hypertrophy of epidermal and tracheal epithelial cells. LdCPV-infected caterpillars had numerous granular eosinophilic intracytoplasmic viral inclusions in midgut epithelial cells. Both LdMNPV-infected and LdCPV-infected caterpillars had atrophy of fat body adipocytes; this change was more pronounced in LdCPV-infected caterpillars. This work provides the first detailed descriptions of these viral infections in European gypsy moth caterpillars using bright-field light microscopy and provides images of normal histology from control caterpillars.