“Normally a biocontrol agent tends to disappear a few years while it settles in before signs of establishment are seen, followed by slow spread, so the project has gone even better than we expected.”
Stephanie says the parasitoid wasp lays an egg in the aphid. When the larva hatches, it eats and eventually kills the aphid host as it develops. In two to three weeks a new adult parasitoid emerges from the dead aphid.
“Pesticides aren’t an option because they would transfer into the honeydew that the aphids secrete, putting nectar feeders such as honeybees, tui, and bellbirds at risk.”
Stephanie says giant willow aphids feed on willow tree sap and have a particularly devastating impact on bee colonies.
“The total impact of giant willow aphids has been estimated to be over $300 million each year.
“It’s vital that we protect our willow trees as they’re an essential part of New Zealand farming for slope stabilisation, flood protection, crop and livestock shelter, fodder, and as pollen and nectar sources for honeybees in early spring.”
Steve says the research has directly benefited beekeepers, river managers, soil conservationists, and farmers.
“Indirectly, the public also benefits as riverbanks become less prone to erosion and fewer pest wasps are drawn to the honeydew secreted by the aphids.
“This research has demonstrated that Pauesia nigrovaria are a highly cost-effective, sustainable, and environmentally sound control method for controlling the giant willow aphid population.”
Monitoring and reporting on this trial will be ongoing, with assistance from citizen scientists across the country.
