3.2.1. When to sample
When trying to detect tracheal mites, sampling time is crucial. Infestation by tracheal mites varies through time. For detection of HBTM in colonies, bees should be collected in winter or early spring when HBTM populations are highest because of the reduced bee brood production. During this time, a high proportion of older, overwintering bees is present in the colonies, and the mites have had a long time to reproduce. The large number of actively feeding mites can cause the tracheae to turn black. Infestation of HBTM decreases in summer due to the dilution of mite populations as they enter the large population of emerging host bees.