Enhancing baculoviruses as biopesticides with the polydnavirus CrV1 gene

Pathogenicity of baculoviruses may be enhanced as biopesticides by introduction and expression of exogenous genes such as those coding for proteins interfering with metabolism, metamorphosis (toxins, hormones, and enzymes), and immune system. The CrV1 gene of Cotesia rubecula polydnavirus (PDV) is responsible for depolymerization of actin in hemocytes, and the abolishment of immune functions such as phagocytosis and cell spreading, thus allowing the successful embryonic development of the parasitoid wasp. Two constructs were prepared using the CrV1 cDNA and the Autographa californica nuclear polyhedrosis virus (AcMNPV) genome: CrV1 driven by polyhedrin (Ac-pPolh-CrV1), and p10 promoter (Ac-pP10-CrV1). Recombinant viruses, in supernatant harvested from Sf9 cells, produced a significant (P<0.01) higher mortality rate in Spodoptera exigua (=76.4%±3.1%SE; n=32), and Sesamia nonagroides larvae (=78%±5%SE; n=30) than that of healthy larvae as controls (=9.58%±4.4%SE; n=32). Mortality rate using wild-type baculoviruses were: in S. exigua larvae, SeMNPV==88.3% ±6.1%SE; n=30 and in S. nonagroides, AcMNPV;=56.2% ±6.2%SE; n=32; SeMNPV==93.7% ±6.2%SE; n=32. Morphological changes were more notorious in Sf9 cells inoculated with recombinant viruses, and S. exigua larvae stopped feeding. Ac-pPolh-CrV1 lacks the polyhedrin gene and produces not occluded virions, therefore, it cannot be used as biopesticide unless it is co-occluded into one polyhedron. Studies to improve our recombinants using other promoters and bioassays in other insect pests are currently underway.