Back in 1988, two entomologists, Joe Lewis and Jim Tumlinson, joined in a project that, for the first time, uncovered the ability of an insect to learn through association.
It was, at the time, not only novel, it was also an out-and-out revelation. An insect — in this case, the parasitic wasp (Microplitis croceipes), which feeds on and eventually kills certain agricultural pests — could learn in a most-basic way. Think Pavlov's dogs, except smaller and buzzier.
From that study and other similar research — by the Defense Advanced Research Projects Agency (DARPA) and the Stealthy Insect Sensor Project at the Los Alamos National Lab, for two — we have spun forward to the point where honeybees now have successfully sniffed out long-buried landmines in Croatia.
That's a long way from that January some 30 years ago when Lewis and Tumlinson released their findings in Nature magazine to the astonishment of many.
"You talk about training an insect, period," Lewis says. "You get the look. The eyes start narrowing. It just doesn't make sense."
Teaching a Bee (Or Wasp)
The whole idea behind associative learning is fairly simple, even if no one dreamed decades ago that insects could do it.
With Pavlov's dogs, when an outside stimulus — a bell is often cited — was associated with food, the dogs salivated. The dogs learned, intuitively, that the bell meant food was coming.
For the Lewis-Tumlinson wasps, various odors that the wasps normally didn't recognize (like vanilla and chocolate) were mixed with something that was associated with the pests that these parasitic wasps were trying to make their hosts. After a very short time, the wasps associated the vanilla (or whatever) with the insects that they wanted to attack and they flew toward the odor. It took less than five minutes to train the wasps, which like bees and dogs have olfactory senses thousands of times more powerful than a human.
As the studies continued, new researchers linked the smell of various chemical compounds in explosives to food. Today, a honeybee trained for just two days can associate the smell of explosives with food and seek out that smell.
Two big advantages to training insects to track odors rather than, say, a dog: They learn faster and there's a lot more of them to teach.
You Can't Put a Leash on a Bee
Releasing a swarm of wasps or bees on a battlefield, or even a now-quiet meadow in Croatia that may be littered with mines, has its challenges, of course. Tracking the insects is foremost among them. It's impossible, as Tumlinson points out, to put chips on each of them. And you can't, as Lewis says, put a leash on a bee.
Still, through devices like drones and webcams and something early researchers called a "Wasp Hound," scientists can trace the insects' movements, in at least small numbers. Lewis' Wasp Hound, about the size of a large coin, contains five wasps, a tiny camera and a computer fan that pulls air through a small hole in the bottom of the device. When the Hound comes near the target smell, the wasps "cluster around that little hole like pigs to a trough," Lewis says.
Another problem researchers face is scale. Training one wasp or one bee at a time can be laborious. Scientists have come up with methods to train more than that. But insects, like some people, learn at different rates, so mass learning is not as accurate.
In addition, bad weather or anything that disrupts the insects' ability to smell can cause difficulties. Research is continuing.
Back to Basics
Tumlinson and Lewis — Tumlinson is a professor of entomology at Penn State, Lewis a retired professor and a research entomologist with the U.S. Department of Agriculture in Tifton, Georgia — never envisioned bees sniffing out bombs. They were looking for ways to control pests biologically, rather than with pesticides. And, in fact, they were very successful at it.
Along with U.K. scientist John Pickett, Lewis and Tumlinson won the 2008 Wolf Prize for Agriculture, considered by many as a type of Nobel Prize in the field. From the official announcement on the Wolf Foundation website, they were awarded the prize "for their remarkable discoveries of mechanisms governing plant-insect and plant-plant interactions. Their scientific contributions on chemical ecology have fostered the development of integrated pest management and significantly advanced agricultural sustainability."
Whether their work eventually will help form the basis of a widespread, practical use of bees and wasps in sniffing out bombs or drugs remains to be seen. Even they have some doubts.
"You can train insects to find a mine. That's not a problem. But then you release them into the field to find a mine. How do you track them?" Tumlinson says. "Unless someone comes up with a small chip so that you can track them with some electronic means, I don't see how in the world you can use them."
Says Lewis: "To move it from the lab to the actual field, you have to scale it up and refine it. But we clearly can see that it can be practical in development. It's technically feasible. It's all on valid science. The ability is there. It's about the demand for it and putting the infrastructure in place for that."
That is a challenge for the next generation of scientists and researchers. The wasps and bees will still be around.