Beetle Farmers 2.0: A Super-symbiont Fungus Supports a Complex Beetle Society
By Jiri Hulcr and Matt Kasson
Eating wood is really tough. Many insects are pretty good at chewing wood with their mandibles, but they can’t produce the right concoction of enzymes to digest the chains of cellulose and lignin. That’s what fungi are good at, and that’s why most wood on this planet is not chewed up, but instead degraded by fungi.
So what’s the best way to utilize wood, one of the most abundant sources of energy on the planet? Join forces! Because insects can chew wood and fungi can digest it, many insect-fungus symbioses have emerged.
Researchers used to think that one such wood-eating relationship existed among ambrosia beetles and their fungus partners. It turns out, however, that none of these ambrosia fungi actually digest wood. In fact, most are relatives of plant pathogens, so instead of digesting cellulose, they are good at getting into freshly dead trees, snatching whatever easily-available nutrients are left in the dying tissues, feeding a generation of their beetle vectors, and getting out and into the next dying tree.
That’s one paradigm down. Now a team of entomologists and mycologists from West Virginia University and the University of Florida has uncovered something unprecedented: There is one group of ambrosia beetles that actually DID figure out how to grow a true wood-digesting fungus. Why is that interesting? Because partnering with such fungi allows them to develop complex social structure with some of the largest colonies of beetles on the earth.
Ambrosia beetles from the genera Ambrosiophilus and Ambrosiodmus have been shown to partner with the white-rot decay fungus Flavodon ambrosius, a relative of bracket fungi, those that are found on old tree snags. The new research has shown that Flavodon is a superior wood degrader. It’s better than most other wood-decaying fungi, and vastly more aggressive and tenacious than any other ambrosia fungus. This beetle “crop” that turns rotten wood into complete animal nutrition over multiple generations allows the beetle adults to stay home and reproduce, and to create truly semi-social colonies with thousands of beetles.
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Jiri Hulcr is an assistant professor of forest entomology at the University of Florida’s School of Forest Resources and Conservation. His team studies wood-boring beetles, tree pathogens, insect symbionts, and their impact on forests and people. Jiri is also increasingly involved in science-policy dialogue and in extension and outreach for the benefit of our forests.
Matt Kasson is an assistant professor of forest pathology at the West Virginia University’s Division of Plant and Soil Sciences. His team studies emerging forest pathogens, insect-fungus interactions, and biological control of invasive plants and insect pests.