Fungi may aid tree-killer beetles in converting a tree's natural defense mechanism against itself.
Millions of conifers have been slaughtered in European forests since the Eurasian spruce bark beetle (Ips typographus) was discovered on February 21. Researchers believe that these bark beetles are involved in the insect's hostile invasions.
This fungi-made perfume may explain why bark beetles swarm the same tree. As climate warming makes Europe's forests more vulnerable to insect invasions, this relationship might help scientists develop new strategies to prevent beetle attacks.
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Bark beetles are a rodent found in the United States that feeds and breeds inside trees (SN: 12/17/10). In recent years, several bark beetle species have attacked forests from North America to Australia, leaving horrific remains in the wake.
Conifers are, in fact, chemical weapons factories. The evergreen scent of Christmas trees and alpine forests comes from airborne versions of these chemicals. However, these chemicals' primary purpose is to trap and poison invaders.
Or at least, that's what they're supposed to do.
"Conifers are stuffed with chemicals and other stuff that shouldn't harm insects," says Jonathan Gershenzon, a chemical ecologist at the Max Planck Institute for Chemical Ecology in Jena, Germany. "But bark beetles seem to not mind at all."
Some scientists have been questioning if bark beetles can help overcome the powerful cone defense system. (SN: 11/30/21) Some types of fungi, including some species in the genus Grosmannia, are always found in association with Eurasian spruce bark beetles.
After 12 days, Gershenzon and his colleagues compared the chemicals released by spruce bark infected with Grosmannia and other fungi to the chemical profiles of uninfected trees.
Jonathan Cale, a fungal ecologist at the University of Northern British Columbia in Prince George, Canada, was previously assumed that invading fungi would no longer alter trees' chemical composition.
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Later investigations revealed that bark beetles can detect many of these fungi-made substances. The group tested this by attaching tiny electrodes on bark beetles' heads and detecting electrical activity as the chemicals wafted through their antennae.
The attractive nature of the chemicals might explain the beetle's swarming behavior, which results in the death of healthy adult trees.
While the scent of fungi might doom trees, it might also result in the deaths of beetles. Beetle traps in Europe currently use only beetle pheromones to lure their victims. Maybe it's possible to combine pheromones with fungi-derived chemicals to make traps more effective.
Cale believes the findings offer a "significant step toward developing new methods to manage destructive bark beetle outbreaks" for other beetle species as well. In the future, mild winters and drought have put conifer forests at greater danger from mountain pine beetle (Dendroctonus pendersoae) invasions.
