Grooming is a VERY important aspect of honey bee health. Latest research shows that Honey bees exposed to Neonicotinoid pesticide aren't good at grooming each other. Apparently the pesticide blocks the part of their nervous system in charge of grooming. Bayer's Neonicotinoid Termiticide called Premise 200 SC works in this fashion. The Imidacloprid substance damages the nervous system in Termites responsible for grooming. Termites pick up parasitic fungi in the ground and are unable to clean themselves which results in colony collapse (NOTE! Colony Collapse Disorder in Honey Bees).
I have made a short video through the observation window in one of my top bar hives hence the bad quality, where a worker bee grooms a Drone :)