Pheromones from tiny beetles could help save Minnesota’s tamaracks

The first sign of an attack is usually a smell, an aroma that can be quite pleasant, like that of a freshly cut Christmas tree. It emanates from some of the deepest swamps and most hidden corners of Minnesota’s forests. But besides that aroma, there’s something else in the air, something sweet for a destructive type of bark beetle. It’s a trail of pheromones signaling that it’s time to feast.

Scientists at the University of Minnesota have identified the chemicals and compounds that larch beetles produce to communicate with each other. The hope is that these compounds can be manipulated to disrupt this communication and slow the insect outbreak that has killed tens of millions of tamarack trees in Minnesota.

“We now know much more than ever before about how these beetles attack trees, signal each other and find mates,” said Brian Aukema, a forest entomologist at the University of Minnesota, whose lab has conducted research on the epidemic. “We are refining and refining our understanding, and if we can understand exactly how this communication signal works, then we can use it for tree protection.”

Until recent years, little was known about the larch beetle, and it was never problematic enough to merit in-depth study. The native beetle is found wherever larches are found, and it has lived in relative harmony with Minnesota’s pines for about 14,000 years, since the retreat of the glaciers of the last ice age.

The reason for the outbreak, Aukema’s lab discovered, was that winters had become shorter and less harsh. The beetles here, in the far south of the boreal forest, now have just enough warm days between deep frosts to reproduce several times. Healthy larch trees can usually regrow a generation of young larvae. But they are defenseless against two or more.

Scientists raced to understand this once-benign beetle and see if anything could be done to keep tamaracks in Minnesota as the climate continues to warm. Disrupting their communication may be one of those ways.

It’s the female beetle that decides which tree to attack, Aukema said.