Microbial Biopesticides: Viruses
Microbial biopesticides known as baculoviruses are a family of naturally-occurring viruses known to infect only insects and some related arthropods. Most are so specific in their action that they infect and kill only one or a few species of Lepidoptera larvae (caterpillars), making them good candidates for management of crop pests with minimal off-target effects.
Baculoviruses used as microbial biopesticides consist of DNA surrounded by a protein coat (nucleocapsid), which is itself embedded in a protein “microcapsule” or occlusion body (OB) that provides some protection from degradation in the environment. Depending on the virus, OBs may contain a single nucleocapsid (a granulovirus, or GV) or multiple nucleocapsids (nucleopolyhedrovirus, or NPV).
Upon ingestion by a susceptible caterpillar, OBs are dissolved within the alkaline midgut, releasing nucleocapsids that infect the cells lining the midgut. The viral DNA replicates in the nuclei of the host cells and then spreads throughout the body of the larvae, essentially turning it into a “virus factory.” The infected insect stops feeding within a few days, dies and disintegrates, releasing billions of new OBs which can be ingested and cause new infection of neighboring larvae.
The granulovirus of the codling moth Cydia pomonella, or CpGV, is a good example of a commercially successful viral insecticide. First discovered in the 1960 s, it is now the active ingredient of about a half-dozen products sold worldwide. Often used in conjunction pheromone-based mating disruption, CpGV limits codling moth populations and damage in pome fruits while preserving beneficial insects and minimizing chemical residues. Although accepted for use in organic farming, most CpGV applications occur in conventional orchards where its unique mode of action can minimize risk of resistance to chemical insecticides.