I've spoken with my local beekeeper. He says bees don't forage in beans, so there's nothing to be concerned about. I haven't dusted anything else, although my neighbor uses it.
My hive is strong and there has been no massive bee kill off due to his or my use of sevin, in fact the opposite seems true, the hive's grown stronger since I got it.
I'm going to spray if I have to use the stuff, in the evenings. I may try soap and water before the pests get bad. I'd rather go the organic route.
I'd always heard sevin broke down quickly and wasn't harmful to humans, especially if applied about a week before harvest. Is there a milder pesticide available?