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EC-sponsored Research on Safety of Genetically Modified Organisms - A Review of Results
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image Risk assessment of the field use of genetically engineered baculoviruses

Background and objectives

Public awareness of the potential negative environmental effects associated with the use of chemical insecticides led to the assessment of the applicability of insect-specific baculoviruses as an ecological approach to eliminate insect pests. Baculoviruses, however, are relatively slow to kill the target insect. It takes several days for baculoviruses to cause a full-blown infection in the caterpillar, and during this time the insects can continue to feed and damage the crop. The efficacy of baculovirus insecticides needs considerable improvement before they can be presented as viable alternatives to chemical agents for pest control.

The aims of this project were to improve the effectiveness of baculovirus insecticides while at the same time maintaining and improving their safety.

  Caterpillar. image Caterpillar.



Approach and methodology

To improve the efficiency of baculovirus insecticides we inserted the insect gene encoding juvenile hormone esterase (JHE) into the genetic material of the baculovirus. The high levels of JHE normally produced at the end of the caterpillar life cycle cause it to stop feeding and turn into a pupa. Causing the baculovirus to produce JHE at abnormal times in the caterpillar life cycle may reduce feeding and induce premature metamorphosis.

To maintain and improve the safety of baculovirus insecticides we removed a virus gene which produces a protein associated with the release of baculoviruses from the dead caterpillars. If the viruses remain within the cadaver they are not spread easily through the environment.


Main findings and outcome

We infected cultured insect cells with recombinant viruses containing the JHE gene. The consequence was high levels of enzyme activity which matched those observed in normal caterpillars just before pupation. In caterpillars infected with the same viruses, elevated levels of JHE were also attained. With some of the viruses the increased levels of JHE did not affect caterpillar development. Other viruses resulted in slower weight gain by the insects. The host range of recombinant viruses was unaffected by the genetic modification. The removal of the virus gene which affects the release of the baculovirus from infected caterpillars resulted in a virus that was less amenable to spread from the dead caterpillar. Thus it is possible to genetically modify baculovirus insecticides and express potential insecticidal gene products in the target insect. It is also possible to limit the spread of the baculoviruses in the environment.


Conclusions

The new baculovirus vectors developed facilitate the rapid genetic modification of the baculovirus insecticides to test genes which encode putative insecticidal proteins. The results suggest that high levels of insecticidal proteins are produced in the virus-infected caterpillars using viruses that cannot easily spread within the environment. This opens the way for further development of baculovirus insecticides.

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Contract number
BAP-0415/0416

Period
January 1989 - December 1990

Coordinator
R.D. Possee
NERC
Institute of Virology and Environmental Microbiology
Oxford (UK)

 
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Partner


J.M. Vlak
Wageningen Agricultural University (NL)

 
 
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