Insect Viruses

Insect Viruses

	Insect Viruses Insect viruses fall into five major groups-1) nucleopolyhedrosis viruses (NPV), cytoplasmic polyhedrosis viruses (CPV), granulosis viruses (GV), entomopox viruses (EPV) and non-inclusion viruses (NIV) Insect viruses, because of their specificity and obligate nature of parasitism on insects can only be mass produced on live insects. The process of production of the bollworm-budworm nuclear polyhedrosis virus (NPV), Baculovirus heliothis consists of raising bollworm larvae on a semi-synthetic diet containing water-based mixture of casein, sucrose, wheat germ, yeast, wesson salts and growth factors.
Alphacel is used as a filler and agar-agar is used to solidify the diet. Chemicals like formalin, sorbic acid, methyl parahydroxybenzoate, aureomycin are often used to inhibit the growth of contaminating bacteria, yeasts and fungi. The diet is dispensed while hot from a large tank by a filling machine into plastic trays and sealed. These are inoculated by caterpillars from an insectary and incubated under controlled conditions to produce a mass of larvae. A known volume of virus is sprayed on the diet which replicates on the caterpillars to the extent of 5000-10,000 times in 5-7 days. The infected caterpillars are suctioned and then macerated with water, filtered, centrifuged, precipitated and spray-dried. After quality control testing, the preparation is packaged and sold under brand names. In the U.S.A., there are several companies producing this virus commercially.
Some of these companies also produce NPV for the following insect hosts: Lymantria, Mamestra, Neodiprion, Orgyia, Pieris, Prodenia, Spondoptera and Trichoplusia. NPVs are most promising because of their safety, virulence and stability. The CPVF, EPV, and NlV are not so promising and they are still being investigated. The first field trial of a genetically improved nuclear polyhedrosis virus of the alpha looper, Autographa californica (AaNPV) that expresses an insect selective toxin gene (AaHIT) derived from the venom of the scorpion Androctous australis was done in 1994.
Earlier results of laboratory experiments with the cabbage looper Trichoplusia ni showed a 25 per cent reduction in time of death compared to wild type virus without alteration in pathogenicity or host range. The results of another field experiment demonstrated that the modified baculovirus was very active, resulting in decreased crop damage and also reduction in the secondary cycle of infection compared to the wild type virus.

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