When beetles attack, lodgepole pines send chemical SOS to relatives, says U of A study

Lodgepole pines can send distress signals warning nearby trees of an imminent attack and urging them to get their defences in place, a new study from the University of Alberta found.

Warning gives trees time to mount defence, helps explain why some are untouched

Lodgepole pine trees being colonized by the damaging bark beetle will send a message of warning by releasing volatile chemical compounds. (Hunter McRae/The Gazette/The Associated Press)

Lodgepole pines can send distress signals warning nearby trees of an imminent attack from mountain pine beetles and urging them to get their defences in place, a new study from the University of Alberta found.

The study, published in the journal Science of the Total Environment, demonstrates that trees under attack release volatile compounds that send a chemical SOS to neighbouring trees. 

But not every tree gets the message, says U of A forest entomologist Nadir Erbilgin, who supervised the study on behalf of the lead researcher, PhD candidate Altaf Hussain. In a new spin on family trees, the chemical distress signals can only be understood by conifers that are closely related to each other. 

Erbilgin said these "kinship" communication networks allow some conifers to survive attacks while their unrelated neighbours remain defenceless. 

"When there are several thousands of beetles attacking at the same time, trees have very little opportunity to respond," Erbilgin said in an interview with CBC Radio's Edmonton AM. 

"When they respond, it is often too late. But the other trees, with their defences already alerted, what do they do? They immediately respond. Basically, the beetles have no chance, they are killed immediately."

I believe that this goes way beyond the pine.- Nadir Erbilgin, University of Alberta forest entomologist

A tree can protect itself from the beetles by producing high concentrations of resin — a sticky sap — that is toxic to the beetle. 

The study is the first to prove that lodgepole pines can communicate in this way, said Erbilgin. 

"The chemicals that we looked at are produced by pretty much all conifer species. Even the non-conifer species, like the apple trees in your backyard, they produce their own volatile chemicals," Erbilgin said.

"I believe that this goes way beyond the pine. We just proved the concept, we just proved that this is possible." 

Dead trees, killed by mountain pine beetles, glow a rusty red colour near Pyramid Mountain in Jasper National Park in Alberta. (Wallis Snowdon/CBC)

The study focused on swaths of forest in Jasper National Park, which is already ravaged by the mountain pine beetle. 

"We thought what was happening in Jasper National Park was a really good opportunity for us," Erbilgin said. "Because if you look around the forest, you see many dead trees surrounded by live trees so there must be a reason why." 

The tiny beetles survive by burrowing under the bark of pine trees and mining the phloem — the layer between the bark and wood of the tree. After the eggs hatch, the larvae feed under the bark, which makes the trees turn red and die. 

The mountain pine beetle has devastated more than 16 million hectares of forest in B.C. and Alberta, in an epidemic that threatens to decimate forests from coast to coast.

Aided by warming winters, the stubborn beetle population continues to migrate further east every year, migrating well beyond its historic range. Scientists have been scrambling for ways to curb its spread. 

'A very good survival mechanism'

Researchers examined the chemical compounds of trees in the park that had survived infestations and found certain "families" were better equipped to withstand the onslaught.

The trees rely on a complicated web of relationships, alliances and kinship networks.

"Chemical profiles are hereditary for plants," Erbilgin said. "It passes from the mother to the children to their offspring, and they are genetically determined in many ways. 

Some trees were ready to defend themselves.​​​​- Nadir Erbilgin

"We grouped [trees] based on their chemical profiles, and then we had a few groups emerge from this field. Some trees were ready to defend themselves." 

By warning her progeny, a mother tree gives her saplings a fighting chance against an attack, in what Erbilgin calls "a very good survival mechanism." 

The "talking tree" theory, hypothesizing that plants and trees send unseen signals to communicate, dates back to the 1980s, Erbilgin said. Similar mechanisms of communication can be found throughout nature: ants, for instance, will release a pheromone to warn the colony of an attack. 

Kinship support had been previously seen through other mechanisms, but this study is the first to show communication through volatile chemicals, Erbilgin said. 

Erbilgin said the study redefines our understanding of pine biology — and could give scientists a new weapon against the infamously hard-to-kill pine beetle.

In theory, researchers could create a chemical message that every tree could decode, Erbilgin said. The concept is promising, but boosting the defences of an entire forest would be costly. 

"I guarantee you we could save the trees — but, again, how much money do we need to spend to induce defences in trees in an area like this?" Erbilgin said. "There are thousands and thousands of hectares of forest." 


Wallis Snowdon is a journalist with CBC Edmonton focused on bringing stories to the website and the airwaves. Originally from New Brunswick, Wallis has reported in communities across Canada, from Halifax to Fort McMurray. She previously worked as a digital and current affairs producer with CBC Radio in Edmonton. Share your stories with Wallis at wallis.snowdon@cbc.ca.

With files from CBC's Emily Rendell-Watson