Why some beetles like alcohol

April 9, 2018, University of Würzburg

If a small beetle dives into your beer, consider giving it a break. Referred to as "ambrosia beetles," these insects just want what's best for themselves and their offspring. Drawn to the smell of alcohol, the beetles are always on the lookout for a new environment to farm. And alcohol plays an important role in optimizing the agricultural yield of their fungal crops, as an international team of researchers reports in the current issue of the journal PNAS.

Ambrosia beetles, which are a large group of several thousand species worldwide, belong to the bark beetles. All species are characterized by the ability to cultivate fungi. The researchers, including Peter Biedermann from the University of Wuerzburg, Christopher Ranger of Ohio State University (U.S.), and Philipp Benz from the Technical University of Munich (TUM), investigated the role played by alcohol in the farming of fungi as practiced by the black timber bark beetle and its fungal crop.

"It has long been known that alcohol is produced by weakened trees and that these trees are recognized and colonized by ambrosia beetles," says Biedermann. Baiting traps with alcohol is a classic way to catch these bugs. "And often, you will find the roughly two-millimeter-long beetles in glasses of beer, when a beer garden is surrounded by old trees," adds Biedermann.

Sustainable agriculture as a recipe for success

Thanks to the results of Biedermann, Ranger and Benz, we now know why alcohol is so attractive to these insects. "An increase in the activity of alcohol-degrading enzymes allows the insects' fungi to grow optimally in alcohol-rich wood, while alcohol is toxic to other microorganisms," says Biedermann. More fungi means more food for the beetles, and more food means more offspring. The beetles and their larvae feed on the fruiting bodies of the fungi, which grow best at an alcohol concentration of about two percent.

"At this level of alcohol, the omnipresent molds, which can also be considered the "weeds" of fungal agriculture, only grow weekly and cannot overgrow the fungal gardens," says Prof. Benz. Given the beetle's evolutionary success, the details of its sustainable farming strategy are worth noting. "For more than 60 million years, the animals have successfully and sustainably practiced agriculture, even though their crop—the ambrosia fungus—is a monoculture." Unlike human farmers, the insects seem to have had no problem with weed fungi becoming resistant to the alcohol.

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