Baculoviruses as biocontrol agents

The use of Baculovirus to control pest infestations

1. Baculoviruses as Biocontrol Agents Sonia John II M.Sc Zoology No:12

2. Viruses that can infect and kill a number of different invertebrate organisms including insects Usually extremely small, and are composed primarily of double-stranded DNA that codes for genes needed for virus establishment and reproduction.  Rod shaped Very stable and may remain dormant in the environment for long period before infecting insects Baculoviruses

3. Pathogenic to several orders of Insects like Coleoptera , Trichoptera , Diptera , Homoptera etc  Most insect baculoviruses must be eaten by the host to produce an infection, which is typically fatal to the insect. Most of the baculoviruses are registered as Biological Insectides

4. The majority of baculoviruses used as biological control agents are in the genus  Nucleopolyhedrovirus . These viruses are excellent candidates for species-specific, narrow spectrum insecticidal applications. Since they persists in the environment for long periods and can multiply rapidly in the host, its use in pest control seems promising They have been shown to have no negative impacts on plants, mammals, birds, fish, or even on non-target insects. 

5. Baculoviruses can be found wherever insects exist. Because rain and wind readily carry baculoviruses from place to place, it is likely that every piece of land and body of water contains some virus particles. Where are they Found?

6. A baculovirus particle consists of a cylindrical nucleocapsid that surrounds the viral double stranded DNA They are often embedded in a crystalline protein matrix called occlusion body/polyhedron made of the protein polyhedrin Because the genetic material is easily destroyed by exposure to sunlight or by conditions in the host's gut, an infective baculovirus is protected by polyhedron   Structure

7. They are  obligate   parasites . The cells of the host's body are taken over by the genetic message carried within each virion . Upon ingestion by an insect, the polyhedra moves to the midgut ,where the alkaline env facilitates the dissolution of polyhedron ,thereby releasing infectious nucleocapsids Life Cycle

8. The nucleocapsids are taken up by the insect midgut cells and then migrate through the cytoplasm to the nucleus. After viral replication in the nucleus,new viral particles are released to the other parts of the insect and the infection spreads. Ultimately the insect, dies.

9. Insects killed by baculoviruses have a characteristic shiny-oily appearance, and are often seen hanging limply from vegetation . They are extremely fragile to the touch, rupturing to release fluid filled with infective virus particles. This additional infective material can infect more insects, continuing the cycle.

10. Pests attacked

11. Baculovirus are slow in killing their targets. Hence to enhance the speed of kill foreign genes were introduced The foreign genes inserted include the Bt toxin gene(which causes feeding cessation), scorpion toxin gene(which brings in paralysis) and wasp toxin gene(which causes low weight gain). Genetic Engineering for Improved Biocontrol

12. In scorpion toxin gene,the gene that encodes the insect- specific neurotoxin produced by the North African fat-tailed scorpion Androctonus australis was cloned into a baculovirus strain This neurotoxin disrupts the flow of sodium ions in the neurons of targeted insects and eventually leads to paralysis and death

13. A gene for a protein toxin of the Straw itch mite, Pyemotes tritici when inserted into the Baculovirus strains lead to the dramatic improvement in the speed of the kill A diuretic hormone gene from a moth, Manduca sexta was inserted into the baculovirus of Bombyx mori . The infected insects were observed to die faster than those not expressing the neurohormone

14. Another approach involved the introduction of a gene that will disrupt the normal life cycle of an insect when it is expressed in the host insect cells During normal insect devpt , a redn in the level of JH in larvae initiated metamorphosis into pupae and leads to a cessation of larval feeding. The redn in JH is due to an increase in the amt of juvenile hormone esterase

15. Therefore the introduction of a gene that would increase the supply of Juvenile hormone esterase when expressed in the virus-infected insect cells is introduced into the baculoviruses . Increase in the supply of juvenile hormone esterase would lower the level of active JH and cause premature cessation of feeding. It is presumed that shortening the duration of larval feeding would curtail the extent of crop damage

16. The usefuless of this approach is being questioned because the effect of juvenile hormone esterase is confined only to the first larval instar .Other stages of devpt are much less sensitive to this treatment A baculovirus engineered to express juvenile hormone esterase enzyme would have to be applied when the majority of the target insect population was in the 1 st larval instar stage which under natural conditions is difficult to achieve

17. Baculoviruses are registered as bio-control agents because of their ability to cause infections in many arthropod species mainly insects. The genetic engineering done in the baculoviruses would enhance their ability as biocontrol agents by increasing the speed of kill of insects CONCLUSION

18. Abrol P.D & Uma Shankar.Integrated pest Management:Principles and Practices.CABI.org Hammock.D.B . Recombinant Baculovirus as Biological Insecticides.Dept of Entomology and Enviromental . Toxicology.University of California. Mishra Seema.Baculovirus as Biopesticide.National Institute of Immunology.New Delhi. www.biocontrol.entomology.cornell.edu REFERENCES