Resistance to chemical pesticides and issues with environmental contamination required further research to explore non-chemical alternatives. Microorganisms used as microbial biocontrol agents provided environmentally friendly alternatives with relatively low risk of development of resistance by insect pests.

Parasitic insects injected a variety of components into the body of their host larvae. This ensured successful development of their progeny by modifying their host’s immune system. One of the major immune responses to microorganisms that were used for biological control of insect pests was the melanization response which involved formation of a dark-brown precipitate which eliminated the pathogen. In various cases, the failure/inefficiency of microbial control agents could be traced back to the immune resistance of host insects.

Using natural components that interfered with insect immune responses could potentially be utilized to inhibit insect immune responses and therefore increase the efficacy of microbial control agents. In this project, the researcher studied the mechanisms of action of a venom protein isolated from a parasitoid wasp in inhibition of melanization and its effect in a genetically modified insect and a biopesticide. They found that:

• Several serum components from the host binded to the venom protein upon exposure, especially those key enzymes involved in the melanization cascade;
• The intact venom protein was required for its mode of action and none of the functional components of the protein on their own were able to inhibit melanization;
• Production of the venom protein in a genetically modified model insect (fruit fly) made it vulnerable to fungal infection due to suppression of it immune system; however, the protein did not have a major effect on the fly’s development or on its parasitoid success in parasitism;
• When the venom protein was produced in a microbial control agent (a baculovirus) it significantly enhanced its efficacy as significantly less virus was required to kill the host compared to the wild-type virus; however, it was found that this enhancing effect may have not occurred in all host-virus interactions

Overall, the outcomes provided evidence that immune suppressors may offer an option in enhancing the efficacy of microbial control agents, either by producing genetically modified insects that were more susceptible to microbial pathogens or genetically modified microbial control agents that had a superior efficacy over wild-type strains. Considering the effect of the venom protein in enhancing the efficacy of baculoviruses, it was recommended that further research into constructing genetically modified baculoviruses based on species present in Australia and testing them against a variety of insect pests, would be worthwhile but required further R&D funding.

This project has been funded by Hort Innovation, using the research and development levies listed below and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.

• Vegetable Fund