Tilba property owner Ron Snape became excited when he discovered black aphids eating the dreaded and noxious fireweed on his property last week.
The aphids are really doing a number on the weeds, with the bugs causing sap to weep from the weeds as they cling thickly to the stems and flower buds. It appears the aphids may have jumped from the pine trees in Mr Snape’s Christmas tree farm to the adjacent fireweed plants.
But now news has come through from invasive pest experts at Eurobodalla Shire Council and the CSIRO that these aphids are probably “generalists” that won’t be able to control fireweed on the larger scale.
Invasive species supervisor at Eurobodalla Council Paul Martin went out to Mr Snape’s property to check out the large aphid and collect samples.
Unfortunately, he does not believe they will be able to be used a biological control and will eventually be brought under control by other natural predators and parasites.
“Aphids are generalists, that cause localised damage at any given site,” he said. “The aphids on Ron Snape’s place appear to have translocated from nearby pine trees to the fireweed, and are doing very well in one paddock.
“While these aphids have not really been noticed here in the past, Kerinne Harvey, research leader and fireweed expert, for the Weed Research Unit of the NSW Department of Primary Industries, said that she’s seen plenty of them before, and that ‘it's mostly just localised outbreaks of aphids and not much actual damage occurs’.
“As positive as their damaging effects appear, and as much as we’d like them to be a natural biological control for fireweed, these wee beasties unfortunately won't be a solution for controlling fireweed generally, and will be brought under control over time by parasitoids such as tiny wasps and predators such as ladybugs.”
Research director of the CSIRO’s managing invasive species and diseases, Dr Andy Shepherd echoed the council officer’s view that this particular aphid was a generalist that itself would be brought under control.
However, work was ongoing into a real biological control being brought over from South Africa where the fireweed evolved, with one likely candidate being the flea beetle that was currently being tested.
“Bear in mind that a biological control uses biological agents from the native range of the pest,” Dr Shepherd said.
“We have funding through the Department of Agriculture and Water and are working with University of KwaZulu-Natal to try and deliver the project.
“The main potential agent we are working with is the flea beetle in the genus Longitarsus. Will be a while before we know how good its potential is as we test it against Australian native plants.”
Mr Snape meanwhile was just excited he was able to find something willing to eat fireweed and will be keeping a close eye on his patch of aphid-affected weeds.
“If it did ever get used as a biological control, I would like to see it named the ‘Tilba Syndrome’,” Mr Snape said.