Good question, no short answer. We train whole colonies. We don't need all of the foragers to ignore everything except the target scent. We need enough of them, so that they stand out from the others. And yes, we have to take particular care not to entrain the bees on ourselves or our vehicles. When conditioning, we work a bit like investigators on a forensic team at a crime scene. It's why we have to use automated training systems. We have to prep the training standards away from the test area. We wear disposable gloves, etc.
Contaminant issues have to be addressed. An example of a fail occurred at SWRI in San Antonio in the early 2000s. A 50 year flood shut down all of the trials by all of a variety of groups looking at insect sentinels. The test field was under water.
There was a small, cinder block building on site that a research group used to test moths and moth pheromones. I had to leave my employee, Scott, at SWRI to attend 50 colonies of bees at our pre-conditioning stockpile yard. The yard was about 1/4 mile from the block building. The only clean water near the stockpile yard was available at the sink in the cinder block building, and the moth folks had all gone home, taking their insects and gear with team. Since it was pouring rain, and since the rented colonies were short on food, Scott's job was to keep feeders full on the 50 colonies while the rain continued to fall.
The feeder syrup was not intentionally spiked with any odor, and bees aren't good at finding pure sucrose syrup, unlike wasps. That's alway puzzled us. Regardless, one day Scott got a call from the SWRI site supervisor, who needed to see him out at the cinder block building. When Scott arrived, he saw a cloud of honey bees hovering outside of a screened vent in the upper, side, corner of the building. Apparently, there was enough moth pheromone in the building, that it contaminated the syrup as he made it up. Scott couldn't smell any pheromone, but he will be the first to admit to not having a very sensitive nose. Apparently, just mixing sugar syrup in a building used to test moth attraction to moth pheromone was enough to contaminate the syrup, which then inadvertently our bees to moth pheromone, and when there was a break in the rain, our bees found the source building. Due to the screen, they couldn't get in.
The site manager wasn't so much afraid or upset as he was amazed at how easily the bees were conditioned to the pheromone of another family of insects.
Jose, it took us years to figure out how to avoid or separate out false positives. It's partly in how we approach every situation, its partially a function of the density of bees at true targets, and it's partially using a variety of tricks and tools to ensure that we don't key the bees into contaminants, mis-signals, etc. For example, when looking for bombs in cars, we find that a few bees always go to shiny parts, like chrome-coated. But far more bees go to vents and leaks around doors, windows, trunks.
We also have been able to separate bees on IED and landmines in areas grossly contaminated with explosive residues - the number of bees 'hitting' on the real targets exceeds those on the false targets. It's a function of vapor concentration. None of this is simple, it's why we went through three years before we finally were able to get this sorted, and after 35 years, we have learned to 'read' the bee behaviors. Still, our bees on target of necessity have to stand out as statistically significant.
All good questions, no simple answer. It's why we always scout a search area before setting up.
Jerry
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