Santa Cruz >> Bark beetles — whose numbers have reached outbreak levels throughout the West — are hard to keep away from trees. One solution may be to confuse them by playing their own sounds, distorted into a maddening cacophony, back at them.
UC Santa Cruz music professor David Dunn, together with forest scientists from Northern Arizona University, is developing a device that disrupts beetles with sound. The three have received a patent for a new technology that takes the calls of beetles and turns them into a chaotic soundtrack that never repeats. The device has shown promise in laboratory settings, where it causes beetles to attack each other — and stop eating, mating and laying eggs. Now Dunn is working on engineering the device into a useful tool for protecting trees from insect attack.
The beetles attacking Western forests in recent years — causing some of most severe insect outbreaks in recorded history — are native species. But drought, fire suppression and climate change have weakened trees, enabling beetles to go from recycling dead and dying trees to gobbling whole hillsides. Scientists have therefore sought ways to slow these infestations, including measures that address whole forests and those that protect individual “high-value” trees on private property or campsites.
Dunn got interested in the early 2000s, when beetles were attacking pinyon pines near his home in New Mexico. A long-time researcher of the sounds of nature, or bioacoustics, he wondered if sound played a role in insect attacks. He started tapping into trees and recording the insects’ sounds, which they produce by rubbing their body parts together. Then, he teamed up with Richard Hofstetter and Reagan McGuire at Northern Arizona University and embarked on a decade-long journey to study the sounds beetles make and whether sound can be used to combat infestations.
To track their behavior, the team invented “phloem” sandwiches, a piece of phloem — the tasty inner bark tissue of trees — stuck between pieces of Plexiglas. They put pairs of male and female beetles in the sandwiches and played different sounds. The researchers put on a range of noises: heavy metal, radio show host Rush Limbaugh and beetle sounds.
The insects didn’t really seem to notice Limbaugh or metal. But when their own sounds played, they started acting weird. One time, the researchers played the sounds aggressive male beetles make into a log. Hofstetter was shocked to see the destruction that ensued.
“All around the log were just pieces of beetles,” Hofstetter said. “For us it was like ‘Wow we can actually change behavior and potentially reduce beetle populations just by playing back their own calls.’”
But the beetles got used to it after time, and returned to their usual cannibalism-free activities. Hofstetter likened it to people getting used to, and eventually not hearing, a train running through their neighborhood. So Dunn came up with a new technology, using ‘nonlinear chaotic oscillators,’ a jumble of wires and dials that uses equations to create nonrepeating synthetic sounds. He combined the synthetic sounds with beetle noises to produce a soundtrack that was both familiar and unfamiliar to the insects.
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The result was unrelenting beetle chaos. Like the log experiment, the new soundtrack triggered aggression. Beetles tunneled around in aimless circles. Some left the log. They stopped laying eggs, eating and mating. And they never could get used to the new noise.
“They go into neural overdrive and just shut down,” said Dunn.
Dunn and the Northern Arizona researchers have received a broad patent for this method of combatting beetles. Most of the work done thus far has been in phloem sandwiches and logs. Now, Dunn and his graduate students at UCSC are working on miniaturizing the speakers that would attach to trees, and enhancing them so that the sounds can spread all the way up trunks.
“These kinds of technologies are interesting and great for the private landowner, or parks and rec agencies that have high value trees they want to protect,” said Jodi Axelson, a forest health specialist at UC Berkeley. But for large-scale protection, she stressed that forest management techniques such as thinning trees are still most important.
However, Dunn is ambitious. He is sure his device can protect individual trees, but he’s also looking to go bigger. Dunn said he thinks the technology could easily scale up to the level of a commercial orchard, by using an FM signal to transmit the soundtrack to receivers on each tree. This could be useful for targeting ambrosia beetles, which threaten agriculture in Southern California. And for forests, he envisions a “sound wall” that could block beetles from travelling to new areas.
He’s energized by the success of his collaboration with the forest scientists. It’s rare that collaborations between artists and scientists occur, let alone produce interesting or useful results, said Dunn. He stressed that artists are not only good at sharing science, but in contributing their creative thinking toward new research.
“My personal interest is … this need for scientists and artists to collaborate,” said Dunn. “We always need to remind ourselves of this larger frame of interconnections that is our true environment. Imagination and alternative descriptions of the world do that.”