@d(sl)obber - not sure specifically, but reading up on it I wouldn't doubt someone close by was using something like Sevin, maybe? This all happened in a span of ~48 hours. From what I've heard/read from other keepers you have to get a live, poisoned bee in the freezer and then send it off to be able to get a viable test done to find the cause. We may try to do that and send it to whoever does that kind of thing.
Gonna get in contact with the Dept. of Agriculture and go from there.