Just curious - I've seen this before on occasion - several bees in the hive or flying in, that have a notably golden yellow thorax. Are they just pollen dusted, or maybe new hatches? In the second photo, there are five - look upper left corner, bottom middle, middle right side, and just above the center (sorry I couldn't get that one to post larger).
(http://s4.postimg.org/o7yero5ix/Yellow_backed_bee.jpg) (http://postimg.org/image/o7yero5ix/)
(http://s16.postimg.org/wx4g70g5d/Yellow_backed_bees.jpg) (http://postimg.org/image/wx4g70g5d/)
From plants with heavy pollen bees will get it all over. if your bees are gentle enough take a Q-tip and lightly swab one. if it comes off on the Q-tip it's most likely pollen. :) d2