Fungi farmer beetles weed out non-preferred crops

Ambrosia beetles farm fungi for food and weed out the kind they don’t eat.

An experiment led by biologist Janina Diehl, a doctoral student from University of Freiburg in Germany, reveals the agricultural aptitude of the fruit-tree pinhole borer (Xyleborinus saxesenii), a member of the ambrosia beetle family. The research is published in Proceedings of the Royal Society.

Ambrosia beetles now join a select group of insects, including leafcutter ants and termites, shown to possess “agricultural abilities”.

The borer beetles are often found in gardens with old trees. They bore into the wood and feed on fungi which grows in the tunnels they create. To early naturalists, the fungi coverings seemed like divine ambrosia, which is how the beetles got their name. 

In the lab, as documented in the new Royal Society report, Diehl had mother ambrosia beetles establish a series of nests with offspring, in which the fungal gardens form. She then removed beetles from some nests, leaving them in others.

After 40 days, the experiment revealed the nests with ambrosia beetles had cultivated and altered the make-up of their fungal gardens.

“You might have expected there to be fewer food fungi in the nests with beetles because they were being eaten, but in fact, the opposite was true; here the fungal composition was clearly shifted toward food fungi,” says Diehl.

In the nests without nurturing beetles, the proportion of weed fungi was significantly higher.

While the mechanisms used by the beetles to grow their food fungi requires further investigation, it appears the entire group of beetles in the nest, including the larvae, work together to care for the fungi. 

Dr Peter Biedermann, a professor of forest entomology at the University of Freiburg and co-author of the paper, says there is a symbiosis between the beetles and fungi.

“Each ambrosia beetle species has its own food fungus. Neither can survive without the other,” he says.

Social behaviour of the ambrosia beetle Xyleborinus saxesenii / Credit: Dr Peter Biedermann

Further research may also provide worthwhile insights for human agriculture, which is struggling with weed resistance, says Biedermann.

“It’s highly exciting for us to see how nature has been doing this for 60 million years. Presumably, we humans can still learn something from these mechanisms.”

Read more: Dung beetles use sky and wind to find direction

Ambrosia beetles themselves have become a threat to agriculture worldwide, and they have also been the focus of research by the Hawkesbury Institute for the Environment at the University of Western Sydney.

The institute says, the beetles are among the insects most frequently moved around the world by international trade.

“Globalisation has dramatically increased the distribution of ambrosia beetles and thus the threat to forest ecosystems, plantations and fruit industries worldwide.

“The rapid expansion of this invasive beetle’s range and the vulnerability of forests to native and exotic ambrosia beetle damage are also thought to be exacerbated by climate change.”

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