Improved techniques to mass produce NPV

By Our Agriculture Correspondent

AMERICAN COTTON bollworm, Helicoverpa armigera, is one of the dreaded pests of cotton, and it has been found to be effectively checked by spraying with a biological organism, nuclear polyhedrosis virus (NPV). The use of NPV to manage the pest has come to stay as an important component of the integrated pest management strategies for cotton, according to Prof. S. Jayaraj, ICAR National Professor at the Agricultural College and Research Institute (AC&RI), Tamil Nadu Agricultural University, Madurai.

A leading cotton IPM specialist, Prof. Jayaraj is advocating an improved mass production technique for NPV. ``It is a simple technology and it can be adopted at village level by trained hands. Enterprising agricultural graduates can take it up as a commercial venture,'' he explains. For mass multiplication of NPV, large scale culturing of Helicoverpa armigera is a pre requisite, according to him.

To establish a laboratory culture, larvae collected from the field or moths collected from the light traps should be used. The larvae collected from the field should be kept in quarantine to eliminate parasitised or diseased insects. The healthy larvae should be taken for pupation. These larvae can be reared on natural diet (soaked Bengal gram seeds) or semi-synthetic diet.

After three to four days of pupation, the healthy ones are collected and washed in soap water. They are then immersed in 0.5 per cent sodium hypo chloride for one minute. Then the pupae should be washed in running water for 15 minutes. These pupae should be shade dried and kept in sterilized vermiculite inside an adult emergence cage.

When the moths emerge, they should be fed with 10 per cent sucrose solution fortified with a drop of commercial multi- vitamin mixture. The adults can be sexed based on the colour of the scale.

The males are plain greenish and the females chocolate brown. Five pairs of adults can be allowed in a wide mouthed plastic jar (15 cm by 20 cm) and the mouth should be covered with muslin cloth. Adult feed should be provided daily in tiny glass vials with cotton wool.

The females will start laying eggs from the third day of emergence. These eggs should be collected daily and kept under saturated atmospheric humidity. The eggs are sterilized in 10 per cent formaldehyde for ten minutes and rinsed in running water for 15 to 20 minutes.

They are then dried in shade. When the larvae hatch, they should be transferred into small trays containing semi-synthetic diet. About 200 larvae can be accommodated in a plastic tray of 26 cm by 16 cm by 6.5 cm, and about 75 g of feed should be added per tray.

They can be reared in the tray till they reach the fourth instars stage of growth, which is the ideal stage for viral production, according to Prof. Jayaraj.

The fourth instars larvae are inoculated by dipping their heads in a suspension of NPV containing the right count of virus.

They are then transferred to individual vials containing the semi-synthetic diet. After five days, the viral infected larvae are collected and suspended in distilled water. The virus can then be purified by simple filtration and centrifuging.

The virus particles will settle down as a pellet. This can be used for spraying on the crop in the evening hours during the 7th week and 12 th week after sowing, according to Prof. Jayaraj..

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