🐛 Viral Biopesticides

This lesson builds core elective concepts in BSc Agriculture with practical applications and exam-oriented clarity.

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Viral Biopesticides

Insect viruses are among the most host-specific biopesticides available, making them exceptionally safe for non-target organisms, beneficial insects, and the environment. The family Baculoviridae is the most important group used in agriculture, comprising Nuclear Polyhedrosis Viruses (NPV) and Granulosis Viruses (GV).

Nuclear Polyhedrosis Virus (NPV)

NPVs are the most widely used viral biopesticides. The virus particles (virions) are embedded within proteinaceous occlusion bodies called polyhedra, which protect them from UV degradation in the environment.

Mechanism of Action

1. Insect larva ingests polyhedra while feeding on treated foliage
2. Polyhedra dissolve in the alkaline midgut (pH >8), releasing virions
3. Virions infect midgut epithelial cells and replicate in the nucleus
4. Infection spreads to fat body, haemocytes, and other tissues via budded virus
5. Larva becomes sluggish, discoloured, stops feeding, and eventually liquefies (melanisation), releasing billions of fresh polyhedra into the environment
6. Death occurs within 5-10 days depending on virus dose and larval instar

Important NPV Species

Virus	Target Pest	Crop
HaNPV (Helicoverpa armigera NPV)	American bollworm / gram pod borer	Cotton, chickpea, tomato, pigeonpea
SlNPV (Spodoptera litura NPV)	Tobacco caterpillar	Soybean, groundnut, vegetables
SeNPV (Spodoptera exigua NPV)	Beet armyworm	Vegetables, ornamentals
AcMNPV (Autographa californica MNPV)	Multiple Lepidoptera	Various crops

HaNPV is the most important viral biopesticide in India, used extensively against Helicoverpa armigera, one of the most devastating polyphagous pests. It is recommended at 250-500 Larval Equivalents (LE) per hectare.

Granulosis Virus (GV)

Granulosis viruses differ from NPV in that each occlusion body (granule) contains a single virion. Key examples include:

• Codling moth GV (CpGV) — the most successful viral biopesticide globally, widely used in European apple orchards
• Plutella xylostella GV — effective against diamondback moth in cruciferous crops

Production Methods

Viral biopesticides are produced through in vivo methods since insect viruses cannot be cultured on artificial media:

• Field collection — gathering infected larvae from the field
• Laboratory rearing — mass-rearing host insects on artificial diet and inoculating with virus
• Semi-industrial production — large-scale insect rearing facilities

Each infected larva of Helicoverpa armigera yields approximately 1-6 billion polyhedra, and approximately 500 larval equivalents are needed to treat one hectare.

Application Guidelines

• Apply during late evening to minimize UV degradation
• Target early instar larvae (first and second instar) for maximum efficacy
• Add 0.1% jaggery or crude sugar as a phagostimulant to enhance ingestion
• Add 0.5% Tinopal (optical brightener) to protect polyhedra from UV light
• Store formulations at 4 degrees C for maximum shelf life (up to 12 months)

Viral biopesticides are ideal for IPM programmes due to their unparalleled host specificity and environmental safety.

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Summary Cheat Sheet

Topic	Key takeaway
Main focus	Viral Biopesticides — Nuclear Polyhedrosis Virus (NPV), Granulosis Virus (GV), production methods, and field application.
Section context	Revise this lesson with the rest of Biopesticides and Biofertilizers for stronger conceptual continuity.