Virus-based strategies for management of insect pests

Baculoviruses are insect-specific viruses that have been studied extensively both as protein expression vectors and as insect pest control agents, and more recently for use in human gene therapy. Baculoviruses are being developed as environmentally benign alternatives to chemical pesticides for management of certain insect pests. To enhance their insecticidal efficacy, baculoviruses have been genetically engineered with genes encoding insect-specific toxins that are active within the hemocoel of the insect. On infection of the insect host, the toxin is produced as the virus replicates, and the infected insect dies from the effects of the toxin delivered by the virus. Baculoviruses have been engineered with genes encoding a variety of insecticidal proteins and peptides. The most effective enhancement of insecticidal properties of the virus has been achieved by introduction of genes into the virus genome that encode basement membrane-degrading proteases. Recombinant baculovirus insecticides have been developed that now approach the efficacy of the classical chemical insecticides.

Baculoviruses

1. Identification of molecular determinants of baculovirus host range

We are interested in determining the genetic basis for the greater virulence of Rachiplusia ou multicapsid nucleopolyhedrovirus (RoMNPV) compared to that of Autographa californica MNPV against specific lepidopteran pests. Understanding the genetic determinants of host range may allow for development of designer baculoviruses for management of multiple pest species in a given cropping system.

Harrison, R.L. and Bonning, B.C. 2003. Comparative analysis of the genomes of Rachiplusia ou and Autographa californica multiple nucleopolyhedroviruses. Journal of General Virology 84: 1827-1842. Output files from selection pressure analyses (1.4 MB).

Harrison, R.L. and Bonning, B.C. 2004. Application of maximum likelihood models to selection pressure analysis of group I nucleopolyhedrovirus genes. J. Gen. Virol. 85: 197-210 Output and data summary files (3.04 MB).

2. Cost-effective production of baculovirus insecticides

In collaboration with Dr. David Murhammer, we are exploring the possibility of producing a clone of the baculovirus Autographa californica nucleopolyhedrovirus that is stable in continuous cell culture and resistant to insertion of transposons. This would allow for cost-effective, large scale production of baculovirus insecticides.

3. Novel insect toxins for pest management

We are working to determine the mechanism of insecticidal action of the protease ScathL, a Sarcophaga peregrina cathepsin L that specifically degrades basement membrane. This protease has potential for use in insect resistant transgenic plants when combined with an appropriate delivery system. We are also working on development of novel aphicidal toxins.

Harrison, R.L. and Bonning, B.C. 2001. Use of proteases to improve the insecticidal activity of baculoviruses. Biological Control 20: 199-209.

Li, H., Tang, H., Harrison, R.L. and Bonning, B.C. 2007. Impact of a Basement Membrane-Degrading Protease on Dissemination and Secondary Infection of Autographa californica Multiple Nucleopolyhedrovirus in Heliothis virescens L. J. Gen Virol. 88: 1109-1119.

Philip, J., Fitches, E., Harrison, R. L., Bonning, B.C. and Gatehouse, J.A. 2007. Characterisation of functional and insecticidal properties of a recombinant cathepsin L-like proteinase from flesh fly (Sarcophaga peregrina), which plays a role in differentiation of imaginal discs. Insect Biochem. Molec. Biol. 37(6): 589-600.

Tang, H., Li, H., Lei, S., Harrison, R.L. and Bonning, B.C. 2007. Tissue specificity of a baculovirus-expressed, basement membrane-degrading protease in larvae of Heliothis virescens. Tissue and Cell 39: 431-443.

Li, H., Tang, H., Sivakumar, S., Philip, J., Harrison, R.L. Gatehouse, J.A. and Bonning, B.C. 2008. Insecticidal activity of a basement membrane-degrading protease against Heliothis virescens (Fabricius) and Acyrthosiphon pisum (Harris) . Journal of Insect Physiology 54(5): 777-789.

Researchers: Nana Chougule

Schematic diagram of hypothesized mechanism of action of basement membrane degrading protease.

4. Risk assessment of a recombinant baculovirus insecticide that expresses a basement membrane-degrading protease

The Autographa californica nucleopolyhedrovirus was engineered to express the proteolytic enzyme Sarcophaga peregrina cathepsin L that specifically degrades basement membrane. This virus is among the fastest recombinant baculoviruses developed to date. We have shown that this recombinant baculovirus has no deleterious impact on non-target predatory insects, and minimal impact on insects that parasitize lepidopteran larvae.

Harrison, R.L. and Bonning, B.C. 2001. Use of proteases to improve the insecticidal activity of baculoviruses. Biological Control 20: 199-209.

Boughton, A.J., Obrycki, J.J, Bonning, B.C. 2003. Effects of a protease-expressing recombinant baculovirus on nontarget insect predators of Heliothis virescens. Biological Control 28(1):101-110.

Nusawardani, T., Ruberson, J.R., Obrycki, J.J. and Bonning, B.C. 2005. Effects of a protease-expressing recombinant baculovirus insecticide on the parasitoid Cotesia marginiventris (Cresson). Biological Control 35(1):46-54.

Sun, X., Wu, D., Sun, X., Jin, L., Ma, Y., Bonning, B.C., Peng, H., Hu, Z. 2009. Impact of Helicoverpa armigera nucleopolyhedroviruses expressing a Cathepsin L-like protease on target and nontarget insect species on cotton. Biol. Control 49 (1): 77-83.