By Brad Haire
University of Georgia
Glen Rains knew that parasitic wasps could be trained to pick
up a scent and stick to it as well as any bloodhound. But wasps
don’t respond to commands like “sic ’em” or “stop.” They can’t
fly well with little leashes, either.
Rains needed a way to keep them focused, contained and mobile
outside the lab. So, he and a colleague invented the “Wasp
Hound.”
The Wasp Hound is a 3-inch PVC pipe about 10 inches long. A fan
and a Web camera closes one end. Inside, a tray places four or
five wasps over the tiny pinhole in the removable white cap
that covers the other end.
This portable nose can monitor the behavior of wasps trained to
respond to a particular scent or volatile compound, he said.
Rains has used trained wasps to detect aflatoxin, a poison
produced by fungi that attack crops like peanuts and corn in
fields and in storage.
“Volatile compounds are released by all organisms, either
directly or by chemical reaction with other materials,” said
Rains, an engineer with the University of Georgia College of
Agricultural and Environmental Sciences.
In nature, a parasitic wasp uses its tracking ability to find
food and hone in on the scents of caterpillars it likes to
inject with eggs. The eggs hatch. The larvae eat the
caterpillars.
The wasp finds the caterpillars, too, by detecting scents
released by plants, often field crops, that the caterpillars
are eating.
The premise of the Wasp Hound is based on the work of Joe
Lewis, a U.S. Department of Agriculture entomologist. Over the
past two decades, Lewis has learned that parasitic wasps can
smell nearly anything and can be taught to respond to smell.
Rains and Lewis use wasps that have been bred in a lab on the
UGA Tifton, Ga., campus. Thousands can be produced each week.
There is nothing particularly unique about the wasps when
they’re born.
But through conditioning them to link a certain smell to food —
in this case, sugar water — they become little bloodhounds.
It takes 5 to 10 minutes to train them. It can take months to
train a dog to consistently pick out one scent.
The conditioned wasps are loaded into the Wasp Hound. The fan
sucks air through the pinhole in the cap. If the scent they’ve
been trained to recognize whiffs through, they will crowd
around the pinhole. If the scent’s not there, they just hang
out.
Through a USB wire, the Web camera sends an image of the wasps
to a computer. There, software analyzes the amount of dark
space created around the pinhole by the wasps against the white
background of the cap.
The software creates a graph that shows the level of crowding,
or the wasps’ response to the odor they were trained to detect.
It doesn’t take long for the Wasp Hound handler to get the
answer.
“This adds objectivity to the process,” Rains said. “In about
30 seconds, we can know if the wasps picked up anything.”
Forensic entomologists have asked Rains if wasps can be trained
to help investigators find clandestine grave sites. He thinks
they can.
The wasps can also be trained to detect explosives, he said.
Once a dog is trained to a scent, it’s tough to train it to go
after another. The wasps in the Wasp Hound can’t be trained to
respond to another scent, either, he said. But wasps are cheap
to produce and are beneficial to farmers.
“Once you’re through with the wasps,” he said, “you can just
let them go.”
A parasitic wasp’s life span is two to three weeks.
The work that went into the Wasp Hound was funded by the USDA,
UGA and the U.S. Department of Defense.
