Much of the world has barely noticed one of 2020's plagues, the locusts devastating food supplies in large areas of Africa and Asia. However, some researchers hope the flying insects' excellent sense of smell can also serve some good, saving humanity from a threat of our own making – unexploded bombs.
According to one theory humans outsourced sniffing to dogs, explaining our poor sense of smell. True or not, we cannot detect the tiny proportion of molecules in the air that might lead us to explosives, but other animals can. Already giant “hero” rats have saved many lives through landmine detection, allowing people in former warzones to safely reclaim their lands.
Professor Barani Raman from Washington University thinks American locusts (whose relatives have the largest known animal genome) have the potential to be even better explosive detectors, having well-studied olfactory systems, easy to observe brains, and the capacity to carry heavy payloads for their weight and recover well from surgery.
To see if the idea had merit Raman first needed to test if locusts can actually smell the relevant explosives. "We didn't know if they'd be able to smell or pinpoint the explosives because they don't have any meaningful ecological significance," Raman said in a statement.
In a paper in Biosensors and Bioelectronics X Raman describes tapping signals in the locusts' brain to show specific neurons are activated on encountering explosive molecules such as TNT. Raman also found locusts can smell ammonium nitrate, the causes of this month’s horrendous explosion in Beirut.
If locusts ever do develop a bomb-detection career path, however, they won’t be the wild locusts ancient prophets fed on in the desert, but artificially enhanced to cyborg status by implanted electrodes, or “biorobotic chemical sensing system,” in the researchers’ words.
Raman and co-authors strapped locusts with implanted electrodes to model cars and drove them around in a box injected with explosive vapors, moving between areas where the smell was strong and weak. The chauffeured locusts’ brains registered how strong the smell was, a necessary step to follow the gradient to the source of a scent.
"You know when you're close to the coffee shop, the coffee smell is stronger, and when you're farther away, you smell it less? That's what we were looking at," Raman said.
Ideally, we might train locusts to associate explosives with food so they can lead us to dangers. Not only would an insect be less likely to trigger an explosion than a rat, but there might be less backlash if deaths occur.
However, having demonstrated the electrodes can measure reaction strength, Raman can map where the smell is strong and weak, something he called a “more sophisticated” version of a coal mine canary. This could lead us to a bomb, even if the locust is indifferent.
So-called “electronic noses” capable of detecting and distinguishing molecules in the air have been advancing over the last two decades, and can often outperform the human nose. However, for many purposes, including this one, they are still far behind animal counterparts, honed by millions of years of evolution.