All of the citations about bees and sense of smell are out-dated, and most are wrong.
We've conducted hundreds of double-blinded trials with a large variety of scents - bees are comparable to dogs in their olfactory acuity.  Far better than humans for most odors.  We routinely work in parts per trillion or lower scent ranges.
For explosives, we know that they can instantly identify break-down products of many commonly used explosives at a few parts per quadrillion.  

The idea that bees have a poor sense of smell, not much better than humans, except for a few pheromones is a misquote of the notoriously poorly designed study of von Frisch and his wife, the work of Ribbands that proved von Frisch was wrong, and then a misquote of Ribbands - all by people who never read the original work of either.
Jerry


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