Mass Multiplication of Microbial Pesticide Production of Helicoverpa armigera Nucleopolyhedrovirus (HaNPV)

Gram pod borer Helicoverpa armigera In India gram pod borer Helicoverpa armigera is the most serious pest of crops in India. It is a polyphagous, major pest of cotton, legume crops like gram, chickpea, pigeon pea, pea, maize, sunflower, tomato and many other agriculturally important crops. Female of this insect lay 200-400 eggs on inflorescence, leaves and pods. The eggs are round bright greenish yellow in colour. Damage is caused by larvae of this pest

Background The virus Helicoverpa armigera nucleopolyhedrosisvirus (HaNPV) that naturally infects H. armigera, has been isolated and is employed as a 'viral insecticide' against this pest. Aqueous suspension of HaNPV extracted from diseased larvae is used in a spray on crops. It is highly specific self perpetuating/ recyclable. The HaNPV has been found to be safe to mammals, non-target insect and environment. It is an important microbial control option of IPM available for H. armigera management.

Symptoms of HaNPV Infection The Helicoverpa armigera larvae infected with NPV become-pinkish /pale in colour. Swell slightly and then become limp and flaccid. In field prior to death, larvae infected with NPV climb up the plant and hang by their prolegs upside down. Tissues get disintegrated and liquefied.

Production of HaNPV Being obligate, virus has to be produced only in live insects. Thus, for the production of HaNPV, either rear H. armigera on large scale or collect the larvae from field and use them for HaNPV production. Collect the 250 larvae (6-7 day old) of H. armigera from field.

Larvae are singly placed in plastic tubes containing food contaminated with NPV. After 7-8 days collect larvae showing the symptoms of NPV infection before they liquefied, in air tight container. Keep this container for 8-10 days to decompose the larvae, so that polyhedra released from infected tissue.

Cont…… Homogenize the decomposed suspension of diseased larvae using a homogenizer. Dilute the homogenized content with small amount of water and filter through two layers of muslin cloth. Little water is sprinkled 2-3 times over the remnants to extract residual polyhedra. For crude preparation the filtrate is diluted with water to make solution of 250 ml. This is known as 250 LE (LE-larval equivalent) HaNPV HaNPV in stoppered bottle, and store in cool and dry place.

250 LE (LE-larval equivalent) HaNPV. The effectiveness of the viral insecticide is critically dependent on the concentration of POB, which is expressed as larval equivalent (LE). A standard 1 LE stock preparation consists of 6 ×109 POBs/ml.

Use of HaNPV in Field The field application rate of 250-500 LE/ha of HaNPV has been recommended for the control of H. armigera by different workers on various crops. The virus is highly specific to target insect. So it has no deleterious effect on non-target organisms and environment

Summary Mass production of HaNPV insecticide is simple and widely produced even at the village level. Healthy H. armigera larvae reared in the laboratory or collected from the fields are fed with a low dose of HaNPV and the virus produced in the insect is harvested. Its concentration is estimated by counting polyocclusion bodies (POBs), which are aggregates of HaNPV particles encased by the viral polyhedrin protein. The effectiveness of the viral insecticide is critically dependent on the concentration of POB, which is expressed as larval equivalent (LE). A standard 1 LE stock preparation should consists of 6 ×109 POBs/ml.

References http://www.fao.org/docs/eims/upload/agrotech/2011/HaNPVmanual-pt1.pdf http://www.kvk.pravara.com/horti/dbtbiocontrol.htm http://www.icrisat.org/what-we-do/satrends /may2007.htm