Drugs present a far less challenging problem, mainly because aromatic, volatile chemicals are often used in their manufacture. For example, dogs may be able to find cocaine by the odor of methyl benzoate. We are currently testing the responses of bees to chemicals associated with the manufacture of drugs. Bees can be easily conditioned to odors that they respond positively toward such as many floral scents, can often be trained to substances that they naturally ignore, and can even be conditioned to seek out some things that they might normally avoid. But, there are some chemicals that induce a strong negative response in bees.
Beekeepers use that knowledge to drive bees out of honey boxes.
The beekeeper pours a chemical on an absorbent pad called a fume pad, sets the pad on top of the box of honey, and the bees quickly leave. Usually, the chemicals that drive bees out of hives have a very strong odor that is easily perceived by the human nose and we also find the odor to be repugnant. Determining that bees have found something of interest presents a different challenge. All of these approaches have and can be successfully used. Tracking of bees over a kilometer has been accomplished by Joe Riley in England.