If you had to sexually attract a brown spruce longhorn beetle, would you know what to do?
Jon Sweeney knows.
Start with a deep whiff of male beetle sex pheromone.
“By itself, it’s not very attractive, but if it’s emitted along with odours that smell like a stressed spruce tree …it increases the attraction five to ten times and brings in both sexes,” he explains. (He describes it as a “piney” aroma mixed with the stinging smell of ethanol.)
“It’s kind of neat because it attracts both sexes, so you can get a measure of the number of females and males in the area.”
You might now wonder why he’s spent his professional career exploring the intimate lives of insects. It’s part of his job as a research scientist at the Atlantic Forestry Centre in Fredericton.
He’s learning more about the brown spruce longhorn beetle in the hopes of preventing or containing outbreaks of the critter, which can devastate forests.
He recently won the gold medal for Outstanding Achievement from the Entomological Society of Canada for his work studying the ecology and management of the brown spruce longhorn beetle in Atlantic Canada.
“It’s a very nice honour. I was very surprised,” he says. “I’m just one little tip-of-the-iceberg guy who happens to do most of the presentations.”
The beetle was discovered in 1999 in Halifax’s Point Pleasant Park. Since then, Sweeney has led the containment program and chaired the science subcommittee that provides critical advice on risk mitigation and regulatory programs.
His team’s work has helped slow the spread of the beetle.
Love traps teach scientists about beetles
He said in Nova Scotia, most beetles are within 120 kilometres of Halifax, but spread over about 10 counties. The regulatory zone includes the entire province.
“There is one small site in New Brunswick, near Memramcook, where brown spruce longhorn beetles have been caught in survey traps,” he says, “which suggests there is a small population established in the Memramcook area.”
Sweeney credits his colleague Peter Silk with blending the alluring perfume that no brown spruce longhorn beetle can deny. Leah Flaherty, a PhD candidate at the University of New Brunswick, also made important contributions.
Most insects emit sex pheromones that only attract the opposite sex. Sweeney thinks it’s different with the beetles because perhaps the females come looking for a mate, while the rival males turn up hoping to steal a lady beetle from the original male.
It could also be that the beetles gather to gain strength in numbers and invade healthier trees.
Once they wander into the love trap, researchers can count the beetles and extrapolate the overall population in the area. That lets them track the beetle’s spread and assess how thickly it inhabits a given area.
Big populations may pose threat to healthy trees
“One of the chief things we learned was that the brown spruce longhorn beetle really does prefer to attack stressed spruce trees. It doesn’t do well in healthy spruce trees,” he says.
A big wind storm, a drought, or losing its needles to a hungry caterpillar can all stress a spruce.
Once the beetles colonize a tree — that means they lay their eggs to claim it and they grow into adults — it “pretty much spells the end for the tree.”
The beetles return year after year until it’s dead and they move to the next tree.
That means experts should pay close attention to forests after the trees have been blown over or weakened to quickly spot a new colony of the beetle.
Hurricane Juan, for example, blew down a lot of spruces and damaged others. That stressed the trees, bringing out the beetles.
“There is a hypothesis that we have that when the populations of the beetle are high, they are able to infest and colonize healthier spruce trees. We think that’s maybe what was occurring in Point Pleasant Park back when the beetle was first discovered,” Sweeney says.
Now he’s looking to develop better techniques for detecting new exotic species, particularly other species of bark or wood boring beetles, that may arrive from Asia or Europe via shipping goods.
Sweeney is the fourth Canadian Forest Service scientist to receive the gold Outstanding Achievement since its launch in 1962.