by Sharon Oosthoek
A wasp native to Ontario may soon be pressed into service as a lead investigator into potential infestations by emerald ash borers.
Trials that University of Guelph researchers conducted and the Canadian Food Inspection Agency (CFIA) partially funded show that Cerceris fumipennis can determine, in as little as half an hour after leaving its nest in search of prey, whether invasive beetles are in the area.
The traditional way of surveying – peering into treetops where the beetles congregate – is expensive, and spotting them can take days. The longer it takes, the more trees need to be felled, or inoculated, to stop the beetles’ spread – also expensive propositions.
The shiny green beetles, which in 2002 travelled from Asia to North America in packing materials, kill ash trees by destroying the water- and nutrient-conducting tissues under the bark. Two years ago, Steve Marshall, a professor of entomology with the University of Guelph, recruited Master’s student Philip Careless to see if the large, darkwinged wasps might function as an early warning system for an emerald ash borer infestation. The wasps do not kill beetles in sufficient numbers to control an infestation, but Marshall suspected that they might just “provide a natural and very low-cost approach to monitoring for emerald ash borers.”
Marshall’s earlier research at Rondeau Provincial Park confirmed that the wasp feeds on jewel beetles, including emerald ash borers. But no one had ever attempted to move wasp nests to areas at risk of beetle infestations to see whether they could be used as mobile surveillance units.
During the summers of 2007 and 2008, Careless used a backhoe to dig up earthen wasp nests in various parts of Ontario at night, when the females remain inside. He then drove them in a pickup truck to high-risk areas such as Windsor, where the first Ontario sightings of the beetles were confirmed in 2002.
The wasps reoriented themselves the next morning and then ventured out to find jewel beetles to bring back to feed their larvae. Many of those beetles were emerald ash borers.
On the basis of the speed of the fastest wasp observed – which flew 33.4 metres per minute – Careless was able to estimate how far a beetle infestation might have spread in any given area by calculating how long the wasp was gone from its nest. So, for example, a wasp that took 57 minutes to forage travelled just over 1,900 metres to catch the beetle and return to its nest. That meant that the beetle was caught within 950 metres of the nest site. Given that nests are spread out at regular intervals in a given area, estimating the extent of infestation and the trees that need to be cut down or inoculated become possible.
But before the wasps can be used as portable beetle detectives, Careless needs to figure out how to move the delicate nests without disturbing them. “The soil moves around a bit and, as [it] settles, the entrance to the [nest] tunnel can collapse,” says CFIA survey biologist Troy Kimoto. “Sometimes females will go back and dig it out; sometimes they’ll abandon it.” This summer, Careless will work with the CFIA to experiment with different ways to keep the females happy in their nests.