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Volume 87 Issue 36 | p. 112 | Newscripts
Issue Date: September 7, 2009

Beetle Chemistry, Walking In Circles

Department: Newscripts
Keywords: Beetle, Insects, Limonene, Toluquinone
Buzz off:
Some ground beetles like this defend themselves with repellent chemicals.
Credit: Courtesy of Athula Attygalle
8736ns_antcxd
 
Buzz off:
Some ground beetles like this defend themselves with repellent chemicals.
Credit: Courtesy of Athula Attygalle

Ground beetles aren't celebrity insects. Unlike ants, Disney hasn't personified them in movies, and considering that they make their homes under logs and tree bark, it's easy to see how the GROUND BEETLE could crawl under the radar.

But a new study by Athula A. Attygalle of Stevens Institute of Technology and colleagues at the University of Arizona and the University of California, Berkeley, just might garner the ground beetle the respect it deserves. The researchers report for the first time that these "cryptic" insects produce a "perfect formulation" of limonene and toluquinone as their natural defense against predators.

Limonene belongs to a group of chemicals called terpenes and has been associated with plants and high-profile pests such as ants and termites. For humans, the chemical has a pleasant orange/lemon fragrance and is frequently used in cosmetics. For creepy crawlers, however, that orange scent is the signal to buzz off or die. The chemical is a common active ingredient in commercial insect repellants, causing the demise of most pests within 15 minutes of exposure.

"We've identified more than 500 compounds in beetles, but we never identified terpenes before," Attygalle says. "These particular beetles do not eat plants, so we still don't know how they have these reasonably large quantities of limonene. They must be biosynthesizing it."

In addition to limonene, the researchers also indentified another obnoxious beetle chemical: toluquinone. "The mixture of toluquinone and limonene makes a very effective formulation" for repelling other bugs, Attygalle says.

Attygalle admits that more research needs to be done on how these insects can carry and store such biologically abhorrent chemicals in their bodies. He also speculates that the chemicals might also communicate as phermones.

"The reality is these beetles have come out with real chemistry formulations—perfect formulations—to get the job done," Attygalle says. "They've had 65 million years to perfect it."

The researchers report their findings in a recent issue of Naturwissenschaften (DOI: 10.1007/s00114-009-0596-8).

Directions please:
Without visual cues for navigating, humans in unfamiliar places tend to walk in circles.
Credit: Istock
8736ns_circlescxd
 
Directions please:
Without visual cues for navigating, humans in unfamiliar places tend to walk in circles.
Credit: Istock

As beetles make a beeline away from limonene, it turns out that WALKING IN CIRCLES is the most likely route for people who have no idea where they are. According to a new paper published in Current Biology (DOI: 10.1016/j.cub.2009.07.053), people, in lieu of reliable signposts such as the sun or the moon, really will walk in circles while navigating unfamiliar terrain.

To test people's ability to walk in a straight line, the researchers plunked down six participants in a forest and three participants in the Sahara Desert. The researchers used a GPS device to track the subjects' trajectories and found that those who could see the sun or the moon were able to successfully navigate the terrain. The subjects who were hampered by a cloudy sky, however, didn't have much luck.

Most of the participants "were not aware of the fact that they walked in circles," says Jan L. Souman, one of the lead researchers. "Our results show that walking in a straight line may seem a very simple thing to do, but it actually involves a very complicated interplay of sensory processing, cognitive strategies, and the motor system. That's what makes this topic so fascinating to us from a scientific point of view."

 

Faith Hayden wrote this week's column. Please send comments and suggestions to newscripts@acs.org.

 
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