nucleopolyhedroviruses

Nucleopolyhedroviruses (NPVs) are a group of large double-stranded DNA viruses in the family Baculoviridae that primarily infect lepidopteran larvae. They are characterized by the production of occlusion bodies, polyhedra, which protect virions in the environment and facilitate transmission. In current taxonomy, most nucleopolyhedroviruses are placed in the alphabaculovirus genus within Baculoviridae.

Virions exist in two forms: occlusion-derived virions (ODV), contained inside occlusion bodies, and budded virions (BV) that mediate systemic infection within the host. The genome is a circular double-stranded DNA molecule typically about 80–180 kilobase pairs in size, encoding roughly 80–180 genes. The polyhedrin (polh) gene drives occlusion body formation, while others such as p10 contribute to particle morphology. The genome includes genes for late and very late transcription, DNA replication, and host interaction.

Life cycle: larvae ingest occlusion bodies; the alkaline insect gut dissolves the occlusion bodies, releasing ODV that infect midgut epithelial cells. BV produced in infected cells disseminates the infection to other tissues, leading to systemic infection. Near the end of replication, new occlusion bodies are formed in the nucleus and released when the larva dies, enabling transmission to new hosts via ingested OBs.

Notable NPVs include Autographa californica MNPV (AcMNPV), Spodoptera frugiperda MNPV (SfMNPV), and Helicoverpa armigera MNPV (HearNPV). NPVs are widely used as biological insecticides because they are highly specific to certain pest species and present minimal risk to humans, livestock, and most non-target organisms. They are commonly used in integrated pest management.