How to introduce varroa mites in colonies?

There are two ways to obtain infested colonies: mites obtained from other colonies can be introduced or the existing mite population can be measured and the colony manipulated to obtained the desired infestation level. Bees can be taken out of a colony and the mite directly placed on its host. This can be done by pouring the collected mites on top of the workers in a cage or by picking mites up one by one with a paintbrush and placing directly on a worker. Time should be allowed for the mite to take refuge under the bees' abdominal plates before placing the latter back in its colony. This method is more efficient than dropping the mites onto the top of the frames since more mites can get attached on their host. Alternatively and if the level of infestation desired is not too different from the initial level of the colony, the latter can be split to obtain the desired level. If the level of infestation is above the desired level, brood combs (in which mites are trapped) can be removed.