What are NPVs and how do they work?

Nucleopolyhedroviruses (NPVs) are naturally occurring, highly effective bioinsecticides against a number of important insect pests. NPV-based insecticides promise a potent and environmentally friendly alternative to chemical insecticides. Some NPVs are capable of killing a large number of different caterpillar species, but most NPVs are highly specific and only target a limited number of closely related caterpillar species. These bioinsecticides are extremely safe and do not harm people, wildlife, or beneficial insects.

The active constituent of NPVs is Occlusion Bodies (OBs). OBs are virus particles that are protected inside a protein matrix. When caterpillars feed on plants treated with OBs (right figure) for that specific insect species they become infected with the virus. Alkaline conditions in the insect’s digestive tract cause the OB protein matrix to dissolve, releasing virus particles that penetrate the cells lining the midgut. Once inside the caterpillar the virus is able to multiply and invade almost every cell in the insect. Subsequently the virus causes the cells of the insect to rupture, killing the caterpillar and releasing an NPV-loaded liquid.

This NPV liquid can be spread around the crop by other insects and/or during rainfall or overhead irrigation. Healthy caterpillars that feed on this liquid will become infected and die. In this manner, a crop can become “inoculated” with NPV to help provide protection against subsequent pest infestation.

NPVs in Integrated Pest Management

NPVs can provide effective control of caterpillars with no impact on beneficial species in the crop. This means that natural predators and parasites in the crop are able to provide ongoing suppression of pests after NPV application. The use of less selective insecticides, while providing good initial knockdown control of caterpillars, can cause subsequent flaring of pests due to the removal of their natural enemies. This is a particularly important consideration in the first half of the season and in crops prone to pests normally kept in check by predation and parasitism.

NPVs in Resistance Management

Some caterpillar species have developed resistance to a wide range of chemical insecticides and to genetically-modified (GM) crops. NPVs are able to control caterpillar populations that have developed resistance to synthetic chemistry and GM crops. They are also a valuable rotational product and mixing partner in resistance management. Current scientific evidence shows that the chance of resistance development to NPVs is extremely low. This means that NPVs can be used throughout the season; early for use in integrated pest management and later as a resistance break or mixing partner with synthetic insecticides.

NPVs in Residue Management

NPVs are non-toxic and non-hazardous which means that farmers can re-enter their fields within a few hours of spraying. Moreover, NPVs degrade in the natural ecological environment thus leaving no residues on crops enabling farmers to manage pests right up until harvest without having to worry about pre-harvest internals or challenges of residues on crops.

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