There is a product sold called, "Bee-Scent," manufactured by Scentry Biologicals, 610 Central Avenue, Billings, MT 59102 1-800-735-5323
I don't know if it works to attract bees to pollinate crops (you dilute it and spray it on the crop) and I don't know how long it lasts, but it works GREAT as a swarm lure.
I pour 2 tsp of the stuff, undiluted, on a paper towel, fold the paper towel and stick it in a zipper-lock sandwich bag. I place the bag on top of the top bars in my box-style swarm traps. It contains the nasonov pheromone.
It costs about $16 per pint and you can imagine how many swarm lures that makes.
I picked it up from Great Lakes IPM, www.greatlakesipm.com