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Science. Why cricket could become the mine-clearing expert

A fast, precise and reliable recognition of the chemical components contained in the air is crucial in medicine (for respiratory infections for example), for homeland security (when searching for narcotics or gunshot residues) or for environmental monitoring ( air pollution, fine particles).

In order to meet these challenges of identifying chemical species, “electronic noses”, “sniffers” are being developed around the world. But, according to researchers at the University of Washington, USA, “despite decades of effort, these mechanical olfactory systems do not match the capabilities of their biological counterparts in terms of sensitivity and product range. chemicals detected.

And even if important advances have been made, there are still constraints to overcome to generate a rich repertoire of chemical detections and to be able to easily deploy these tools in the field. The detection of explosives, drugs or cancers by automated tools is therefore not for now.

But, in a recent article published in the Proceedings of the American Academy of Sciences (1), these Washington scientists explained how they hijacked the crickets’ olfactory system. They have indeed led the insect to detect explosives not only different, but in record time.

“We didn’t know if the locusts would be able to smell or locate the explosives because, in their environment, they have no reason to perform these tasks! In fact, it was quite possible that they did not care much about the clues that are, for us, interesting, ”explain the researchers in a press release from the University of Washington.

A locust sitting in a vehicle

It is by observing the cerebral reactions of locusts that biologists have been able to determine what they smell in different contexts. They first tried to see if the insects picked up tiny concentrations of explosive products. The locusts were exposed to vapors of trinitrotoluene (TNT), dinitrotoluene (DNT), cyclonite (RDX), pentrite (PETN) and ammonium nitrate, a diverse cocktail of highly explosive substances commonly used.

“Most surprisingly, we could clearly see that the cricket neurons reacted differently to TNT and DNT, as well as other explosive chemical vapors,” the scientists add. Not only did the locusts smell the explosive, but the way their neurons reacted helped to discriminate between the chemicals detected.

Most surprisingly, cricket neurons react differently to TNT and DNT.

But how to know the concentration of the analyzed product? “The smell of coffee is the same whether it is inhaled in different places, different environmental conditions, different temporal contexts or under different stimulation dynamics (deep or normal inhalation). While this pattern recognition feat is still difficult to achieve in artificial chemical detection systems, it occurs naturally in most insects, for their survival,” explain the authors in their publication.

So the explosive vapors were injected, through a hole, into a box where the cricket sat in a tiny vehicle. As the cricket was driven and sniffed different concentrations of vapours, the researchers studied its odor-related brain activity. And, again, the signals in the insects’ brains reflected these differences in concentration of volatile substances.

An unprecedented nanosurgery procedure

The next step was to optimize the crickets’ brain activity transmission system. There, it’s a little more invasive and you don’t find a neurosurgeon specializing in locusts every day! However, in order to harm the locusts as little as possible and keep them in a stable state to accurately record their neural activity, the team developed a novel surgical procedure. It results in fixing the detection electrodes and the radio transmission system in such a way that they do not hinder the movement of the locusts.

With their new instrumentation in place, “the neural activity of a cricket exposed to an explosive odor was resolved into a discernible pattern specific to the odor.” In short, the locust is able to detect the explosive and identify it in half a second. “Now we can implant the electrodes on the locusts and transport them to specific environments,” the authors say.

Brain activity related to odors

It would therefore not be very surprising to see a demining brigade land one day with a squad of locusts! “It’s not so different from the time when coal miners used canaries to avoid firedamp or the fumes of carbon monoxide, this deadly odorless gas”, conclude the biologists. Or how we go from canaries in the mines to locusts that are demining!

Disease detection dogs. Locusts aren’t the only ones used for their remarkable flair. We all know the customs dogs who, in lack of drugs, are trained to find them in vehicles or on humans. Even more surprisingly, they are used to detect cancers. The biology of some tumors means that markers are found in perspiration or in bodily fluids. Dogs smell these substances with their noses, even in low concentrations. More recently, researchers from the University of Poitiers launched a research program in November to train dogs to detect, always with their flair, carriers of Covid-19.

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