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GOVERNMENT AND SOCIETY Bomb-sniffing bugs materials scientist at Pennsylvania State University, points out that mined areas are often “filled up with bushes and trees modulating typically uneven ground,” he calls the recent work “an excellent conceptual effort.” Physicist Michael Fitch of the Applied Physics Laboratory at Johns Hopkins University says that problems with the resolution and specificity of LIDAR are the major obstacles restricting the usefulness of the bee system. “With a better bee detector, this idea shows promise
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From forgotten landmines to suicide bombers, a grim list exists of uses for instruments that can detect explosives reliably and rapidly. Recently, several groups have reported their novel efforts to use insects, which have exquisitely sensitive olfactory systems and can learn to respond to almost any chemical, to identify explosives. To detect and quantify the insects’ responses, the groups designed systems that creatively meld natural insect ability with modern technology. However, despite some tantalizing early results, these strategies must clear several hurdles before insects can be effective detectives in the search for hidden explosives. Jerry Bromenshenk is leading a multi-institutional effort to use honeybees to find buried landmines, which kill tens of thousands of people each year worldwide. He and his colleagues at the University of Montana, Montana State University, and the National Oceanic and Atmospheric Administration’s Environmental Technology Laboratory fed bees sugar syrup while exposing them to 2,4-dinitrotoluene, the explosive commonly known as DNT and often found in landmines (Opt. Express 2005, 13, 5853). The bees quickly learned to associate the smell of the explosive with food. When they were released over a test minefield, they hovered longer over spots that emitted explosives-tinged vapors. By scanning the field with light detection and ranging (LIDAR), a laser-based technique similar to radar, the researchers created a “bee density map”. The areas of high bee density matched the spots where chemical measurements indicated that landmines were buried. However, LIDAR cannot distinguish between bees and other obstacles in its path, and this forced the research team to conduct the test on a flat, neatly mowed field. This limitation precludes the use of their current system on realworld terrain. Although Craig Grimes, a
Bees and moths may help researchers learn how to better detect explosives.
for humanitarian de-mining operations,” says Fitch. Bromenshenk and his group readily acknowledge the problem of nonspecific detection, so they have developed a modified laser-based sensor that, according to collaborator Joseph Shaw, “has been shown to be successful at picking out the bees from the background.” He adds that the sensor will be described in an upcoming paper that has been accepted by Applied Optics. At a U.S. Department of Defense conference held in November 2001, Kevin Daly at West Virginia University and his colleagues at Sandia National Laboratories in New Mexico and Ohio State University tested an explosives sensing device that is part machine and part moth (IEEE Trans. Instrum. Meas. 2004, 53, 1113). They placed 10 Manduca sexta moths—5 of which were trained to twitch their feeding muscles in response to an explosive chemical— in a small wind tunnel and attached
electrodes to the moths’ feeding muscles to record their responses. When the trained moths out-twitched the control moths, the machine indicated the presence of explosives. Fitch says that some aspects of the moth setup, including the relatively short lifetime of the insects (~2 weeks with the electrodes in place) and the size and weight of the sensing equipment, are impractical, but he praises the group’s efforts to use an objective electronic measure of the moths’ behavior. “This [experiment] is an important step forward in generating electrical responses directly from insect sensors,” says Fitch. According to Daly, the device is not yet reliable enough to use in the field. He explains that a complex behavior such as feeding is affected by many internal and external variables that are difficult to control; for example, as moths age, their olfactory systems become less sensitive. However, he notes that other currently available explosives-sensing techniques suffer from similar problems. “The sense of smell of all animals [including dogs] declines with age. Even the electronic dog nose has similar use-related problems,” he says. He plans to reduce variability by directly recording signals from the sensory neurons in the moths’ brains. In a third effort, soon to be published in Biotechnology Progress (doi 10.1021/bp050164p), researchers at the University of Georgia and the U.S. Department of Agriculture have trained wasps to detect explosives, plant pathogens, illegal drugs, and buried bodies. The wasps are housed in a ventilated cup containing a camera that records their behavior. Fitch says, “I think the dream of research of this kind is to understand the mechanisms of biological chemical detection and to copy them cheaply.” People may never see insects sniffing their luggage at the airport, but these ideas may teach scientists how to build better explosives detectors. a —Karen Ross
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