"After that, reliability of concentration for rats as well as trainers goes down," Weetjens said. This isn't a problem, he notes, since well-rested, replacement rats are available.
Currently the company has more than 100 rats in different stages of training at its facility in Tanzania, north of Mozambique.
Rats begin training at the age of five weeks when juveniles are weaned from their mothers. A positive reinforcement method known as clicker training is used. When the animal does something right, the trainer clicks a small, handheld noisemaker before giving the rat a piece of banana or peanut as a reward. (The same method is often used in America to train dogs in obedience schools.)
The company says the rats learn the desired task relatively quicklybetween six to ten months.
"We now have some fourth-generation domestic animals. And generation after generation, the animals learn faster," said Weetjens. "It is too early, though, to conclude if this is due to selective breeding or to a more established training method and [increased] skills of the trainers."
After an animal has been fully trained, a series of blind tests are conducted during a six-week period. If the rat passes, it is then licensed for de-mining operations.
APOPO plans to use its trained rats elsewhere, including Angola, Cambodia, and Bosnia.
Bees and Bombs
Meanwhile, University of Montana researchers in Missoula have trained honeybees (Apis mellifera) as an efficient and low-cost means to screen large areas for hidden explosives.
The researchers note that most landmines and buried unexploded ordnance (UXO) leak explosives into the environment. During their tests, honeybees swarmed areas where explosive residue was present.
The insects had a 98 percent success rate in tests performed last year. Researchers said the location of the residue can be mapped to provide a picture of the extent, location, and density of bomb-contaminated areas.
"The beauty of this approach is that bees are indigenous to every climate on Earth, and there are beekeepers everywhere," said Susan Bender, a chemist at Sandia National Laboratories in Albuquerque, New Mexico, who worked on the project.
"You wouldn't need a million-dollar piece of equipment and extensive training to use it," she said. "The countries where landmines are a problem typically don't have those kinds of resources."
A hive of 40,000 to 65,000 bees costs around U.S. $100 and can be trained in as little as two hours, according to researchers. Now funding is needed to go to the next step, Bender said, so tests in a real mine field can be conducted.
Bee colonies can also signal other environmental anomalies, including chemical weapons attack, through electronic counters that monitor the number of bees exiting and entering a hive. Unusual activity signals environmental change.
Samples collected from hives, like wax, honey, and pollen, can also highlight environmental contaminants in an area.
Training bees is similar to training dogs. Bees are conditioned to associate an odor, such as the explosive materials TNT, DNT, and RDX, with a reward. In practice sessions, a sugar-water feeder and traces of explosives are set up near a colony. As the bees feed, they begin to associate the explosive's odor with the food source.
As foragers, the bees will search an area for similar odors and continue to look for hours, or even days, with appropriate reinforcement.
Bees also train each other. For example, if multiple hives are needed in a large area, only one needs to be trained. Researchers say the bees from the trained hive will naturally recruit and teach others.
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