Any oil could cause harm to bees. Like other insects, bees' respiration is through openings in the body, not through noses. Stop up those holes with oil and you kill the insect. That's why oil is effective against white flies, thrips and such that are otherwise difficult to kill. Of course, the oil has to be applied directly to an insect for that to work. There's no residual effect, by which I mean applying oil to flowers or leaves that an insect contacts has no effect.