Transmission Dynamics Of Helicoverpa Armigera Nucleopolyhedrovirus And Construction Of A Recombinant Virus Expressing Superoxide Dismutase

There are two chapters in this thesis. In chapter one we reported the horizontal and vertical transmission dynamics ofwild-type Helicoverpa armigera single-nucleocapsid nucleopolyhedrovirus (HaSNPV)and a genetically modified variant (HaSNPV-AaIT) with enhanced speed of actionthrough the expression of an insect-selective scorpion toxin (AaIT). In caged fieldplots, horizontal transmission of both HaSNPV variants was greatest when inoculated3rd instar larvae were used as infectors, intermediate with 2nd instar infectors and thelowest with 1st instar infectors. Transmission was greater at a higher density ofinfectors (1 per plant) than at a lower density (1 per 4 plants); however, thetransmission coefficient (proportion of new infections per infector) was lower at thehigher density of infectors than at the lower density. The use of HaSNPV-AaITexhibited in a significantly lower rate of transmission than HaSNPV-wt, both in cagedfield plots and in the open field. In the laboratory, the vertical transmission ofHaSNPV-AaIT from infected females to offspring was 16.7 ± 2.1%, which wassignificantly lower than that of HaSNPV-wt (30.9% ± 2.9). No vertical transmissionfrom males could be demonstrated. Likewise, in the field, vertical transmission ofHaSNPV-AaIT (8.4 ± 1.1%) was significantly lower than of HaSNPV-wt (12.6 ±2.0%). The results indicate that the recombinant virus will spread less in H. armigerapopulation than the wild-type virus. As a result, the recombinant virus is impaired inits ability to maintain itself over multiple insect generations, potentially affecting IInegatively its long term effectiveness compared to the wild-type virus, butcontributing positively to biosafety. Some kind of phenolase secreted by cotton glands, which generate free radicals,dramatically diminish the infectivity of baculovirus significantly on cotton surface. Inchapter two we analysised the characteristics of sod gene sequence of HaSNPV andcompared its sod-coding product with those of other 13 baculoviruses. The sod geneof HaSNPV was further expressed in E.coli DH5α and the catalytic activity of itsproduct had been detected. Bioassays indicated that SOD-additive HaSNPVsuspension has a significantly higher efficacy to kill the bollworms feeding on cottonleaves than HaSNPV alone. Two recombinant vectors were constructed to obtain tworecombinant viruses in which the sod gene was deleted or a sod-polyhedrin fusiongene was inserted.