Inscentinel is a UK based firm that has developed a process for training bees to sniff bombs. Their technique is based on the fact that bees are highly sensitive to odors. Accordingly, the sensitivity of bees can be harnessed for any application that requires odor detection.
Their Inscentinal website notes, "Insect olfaction and the bees' capabilities represent an effective, sensitive ready-made sensing system that can be tapped into using innovative technology and protocols. Inscentinel uses the honeybees as sensitive, vapour detecting micromachines"