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Researchers launch acoustic offensive

Bark beetles' own sounds manipulated to disrupt mating

Capital Press

Bark beetles live in a dark and smelly environment, so entomology professor Rich Hofstetter figured they must communicate by sound.

If he could disrupt how they communicate, he could disrupt their lives. Barely a quarter-of-an-inch long, bark beetles mass by the thousands to tunnel through millions of acres of trees already stressed by drought and overcrowding.

Hofstetter, at the Northern Arizona University School of Forestry in Flagstaff, has been listening to the sounds of the Ips bark beetle, which feasts on ponderosa, piñon and lodgepole pines. The Douglas fir beetle -- Dendroctonus pseudotsuqae Hopk. -- common in the fir forests of the far West, is in the same genus as the Ips, so his work should translate to those pests as well, he said.

"We have discovered that bark beetles have a wide repertoire of sounds they use," Hofstetter said. "As we have manipulated those sounds, we have seen a direct effect on their behavior."

Early attempts to disrupt the beetles involved using tiny speakers to pipe sound into samples of beetle-infested pine trees. Hofstetter and his associates first tried using rock music and recordings of Rush Limbaugh commentary in reverse.

The researchers saw little effect from that plan of sonic attack, but when they started manipulating the beetles' own sounds and piping them back into the wood, the results startled them.

"We could use a particular aggression call that would make the beetles move away from the sound as if they were avoiding another beetle," Hofstetter said. "Or we could make our beetle sounds louder and stronger than that of a male beetle calling to a female, which would make the female beetle reject the male and go toward our speaker.

He found he could disrupt mating, tunneling and reproduction and even make the beetles turn on each other, which normally they would not do, he said.

How to bring that acoustic attack into the real-world environment is proving problematic, he said. It turns out that bark is an excellent sound insulator.

"We need to bypass the bark," he said. "We have no means of broadcasting."

Even ultrasound penetrates only 1 centimeter into the bark.

The team of researchers is developing a prototype and pursuing a patent for the discovery.

"When it comes to a marketable product, someone else needs to do it," Hofstetter said.

"At this point we're looking at protecting high-value trees in parks and monuments, and we're working on landscape applications. We'll attach the device when the beetles fly and when they attack trees."

As part of the research, some students are exploring what frequencies the beetles hear and trying to find where the beetles' hearing sensors are. They're also looking in the role that fungi and mites play in how insects feed and colonize trees.


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