One sticky afternoon last summer, I picked my way through yellow-green grass on the slopes of Humphreys Peak, close to Flagstaff, with Richard Hofstetter, a beetle expert at Northern Arizona University. Looking up the mountain, we could see the skeletal frames of dead trees amid evergreen forest. We entered a stand. The ground was a mess of lifeless branches. Douglas, corkbark, spruce—about half the conifers were dead or dying.
Hofstetter cut a neat rectangle into the spongy surface of a fallen tree and peeled back the bark. Spruce ips, a species of bark beetle, had carved a delta of channels into the underside to feed off the tree’s sap. When enough beetles take up residence, the host tree is overwhelmed and dies. Due to recent droughts, which weaken the trees, and mild winters, which bark beetles prefer, western forests covering an area the size of Maine are under invasion. In the worst-hit regions, like Colorado and British Columbia, entire forests could be reduced to grassland—victims of the largest insect infestations ever to strike North America.
Hofstetter and his colleagues believe they may have found a way to halt this plague: by driving the insects crazy. For years, entomologists have studied the chemicals that the beetles release for mating and communicating, hoping that they could be manipulated as a deterrent or used for control. This approach has had limited success. But in early 2005, Hofstetter met Reagan McGuire, a former truck driver and pool hustler who had quit his job and enrolled at NAU. McGuire had been thinking a lot about the bark-beetle epidemic, and he came up with a novel idea: perhaps a military crowd-control device he had read about, which emits powerful pulses of sound, could be used to kill the insects. Most scientists would have politely ushered him away, and Hofstetter admits he was hesitant. (“He looked at me like I was crazy” is how McGuire remembers it.) But McGuire convinced the entomologist that the idea might have merit, and the two started to collaborate, with McGuire working as a research assistant.
The military technology, it turned out, didn’t have much practical application. But a little Googling on the subject of beetles and acoustics led the two to David Dunn, an avant-garde composer and collector of animal sounds. Dunn had inserted microphones into the pinyon pines that surround his home in Santa Fe and recorded a CD of the noises they captured. Amid the gurgling of pine sap and slow flexing of the trees can be heard a stream of chirps: the calls of pinyon engraver beetles. The recording marked a turning point for Hofstetter. He and his colleagues had been so focused on finding a chemical deterrent that they hadn’t given much thought to exploiting the beetles’ acoustic abilities. Yet Dunn had captured what sounded like a complex communication system. Somewhere in that entomological language, Hofstetter realized, there might be signals that could be used to disrupt the beetles’ behavior.
McGuire began his search for a sonic weapon by bombarding the bugs with Guns N’ Roses songs and Rush Limbaugh shows in his laboratory. He later got better results using the aggression calls made by the male insects (recorded with Dunn’s help) together with artificial squawks and bleeps of the same frequency. When I visited Hofstetter at NAU, the result was booming through speakers around his lab. The effect it has on the beetles is extraordinary. Hofstetter told me that he had witnessed a pair mate and then, after the sound was switched on, watched as the male ate the female. Nothing like it had been seen before. “People from all over the building were coming in to look,” he said.
In one experiment, the team had placed a beetle on a thin slice of pine sandwiched between two clear panes of Plexiglas. Days before I arrived, the sound had prompted the distraught insect to try to escape by tunneling through the Plexiglas. I asked McGuire if he still had that experiment set up. He paused as he handed it over, looking down at the pane: “Wow. He got out.” In the middle of the Plexiglas was a tiny hole, and no sign of the beetle. McGuire grinned. “We drove him crazy.”
The team plans to try out a version of this technology in the spring. Dunn showed me a car-stereo speaker he’s been testing, which can produce the high-frequency sounds that beetles hear. He described how he had screwed the speaker into a pinyon pine and listened as the output reverberated up and down the trunk. The team believes the device can be used to pump McGuire’s sonic deterrent into vulnerable trees. Fitting every tree in a forest with a speaker would of course be impossible. But if the sounds prove disturbing enough to drive beetles out of the trees, or to deter new arrivals from burrowing into the bark, a ribbon of trees equipped with these cheap devices could form a kind of acoustic firebreak. Enough, perhaps, to protect some of the many millions of acres of still-healthy forests from the advancing beetle armies.
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