Checking a menace

A VIRUS that can be used to manage Helicoverpa armigera, the insect whose caterpillars or larvae have long ravaged crops, has been developed by entomologists at the Crop Protection Division of the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Andhra Pradesh.

Helicoverpa has for long caused damage to chickpea, the most important post-monsoon crop in Andhra Pradesh. The farmers feel that this pest has affected yields.

ICRISAT scientists conducting the experiment tried four different treatments on plots of high-yielding varieties of chi@kpea. One plot was treated with a neem-based botanical insecticide, the second with nuclear polyhedrosis virus (NPV); a chemical insecticide was tried on the third plot and the fourth was left without any treatment at all. Pheromone traps were used to monitor pest incidence, and bird perches provided to encourage such predatory birds as the drongo or'king crow'.

The NPV particles are ingested by larvae as they voraciously feed on sprayed leaves. Infected larvae become sluggish, stop feeding, and eventually die. They are often found hanging head downwards from chickpea plants. The cadavers are full of brown liquid which contains the virus particles. If dead larvae are crushed and mixed with water, the resulting mixture can be used as a cheap insecticide. The virus is inactivated by sunlight, so the mulch should be mixed with stabilisers, and sprayed on to the plants after sunset to ensure its-effectiveness.

The experiments showed that spraying with NPV is not only economical, but is also an environmentally sound strategy.