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Production of Nuclear Polyhedrosis Virus (NPV) by using field collected larvae of Helicoverpa.

Production of Nuclear Polyhedrosis Virus (NPV) by using field collected larvae of Helicoverpa.


Introduction:

Helicoverpa armigera is a major pest of the different crops. The pest is active through out the year. In spite of frequent chemical spraying, crop losses in India are still severe as the pest resistant to insecticides. A new idea for Integrated Pest Management (IPM) is use of naturally occurring disease of Helicoverpa armigera the (HNPV).

 Nuclear Polyhedrosis Virus (NPV) : Importance features of NPV are

  • Occluded (rod shaped) singly or in groups in polyhedral (many sides) inclusion bodies.
  • Site of multiplication is cell nucleus of epidermis, fat body, blood cells and trachea.
  • Wipfel  krankheit  or tree top disease: Diseased larvae not able to feed, move to the top of the tree or plant and hang inverterdly and die.

Collection of Insect

  • Healthy larvae should be collected in cell walls from any infested fields.
  • For more HNPV yield, larvae selected for production should be fourth instar.

Insect rearing

  • Optimum rearing condition such as 24-360 C temperature are required for HNPV production.
  • Food should be available all the time
  • Cleaning the trays and equipment before rearing is necessary to avoid the build up of contamination by protozoa and bacteria.
  • To prevent oviposition by flies on dead larvae.

 Inoculation of virus

  • The larvae are supplied with well soaked 2-3 virus inoculated chickpea seeds.
  • Care should be taken to thoroughly mix the inoculum with chickpea seeds.

Virus harvesting

  • The infected larvae to die naturally in 4-6 days. The virus completes its life cycle to achieve maximum virus production.
  • Larvae with clear symptoms of NPV should be collected at or soon after death leaving those infected with other pathogens. Infected
  • Larvae become pinkish white especially in the ventral side due to accumulation of polyhedra.
  •  In advanced stage larvae become flaccid the skin becomes very fragile and eventually rupture.

Processing virus

  • Blind the dead larvae in a suitable blender to crush the insect tissue and release the NPV.
  • Collect the material washing with distilled water and filter through a muslin cloth to remove the remain parts of larvae body.
  • The solution is centrifused at 2500 rpm for 15 minutes to separate virus from the homogenous liquid.
  • After centrifugation the liquid which is turbid and loose on the top of the tube is poured off and the paste like substance at the bottom with full of NPV is saved.

Measuring the quality of virus

  • Measure the quality of virus by Haemocytometer.
  • Either dark field or phase contrast microscope is needed to count the polyhedral inclusion bodies (PIB) using a Haemocytometer.
  •  The dose of virus is pessed as larval equivalent(LE) and one LE is 6 x10POB.
  • One LE can be had from three fully grown up and virus infected larvae.

Application

  • Spraying the NPV late in the day after peak sunshine to improving the effectiveness of the NPV.
  • Adding UV absorbents use of 1 ml of robin blue nil to a liter of spray solution has been reported as improving the effectiveness of the NPV.
  • For gram, pigeonpea and cotton HNPV should be used at250-300LE, 500LE and 250LE/ha.

 

 

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Please note that this is the opinion of the author and is Not Certified by ICAR or any of its authorised agents.