We have found that bees can be trained to find explosives, drugs, and military unique chemicals. We are investigating whether they can detect explosive vapors at concentrations given off by leaking landmines. We know that they can detect the odor of DNT, a common explosive, at sub part per billion levels, and possibly lower. Training bees to find things by odor is similar to the training that dogs receive to find drugs or explosives. Dogs are conditioned to expect praise and attention or play when they find an item of interest, bees are given a rich syrup reward.
Bees can find things by odor or visual clues or both.
One of the videos on this web site shows a bee flying through a maize. She is following a series of dots in the expectation of finding a syrup reward at the end of the maize. Because explosives are not very volatile, they do not provide much of a signal. Even dogs and sophisticated instruments have problems detecting trace amounts of these substances. Detecting more volatile chemicals is easier.