How many mites to introduce?

The number of mites to introduce in colonies depends on the experiment performed. There are several factors to take into account:

·   The statistical relevancy: a minimum number of successful infestations must be obtained (see the BEEBOOK paper on statistics (Pirk et al., 2013)).

·   A higher number of mites introduced decreases the importance of resident residual/local mites.

·   The infestation level depends on how long the colony should survive: the more mites are introduced, the quicker susceptible colonies might collapse.

·   The method of introduction: introducing mites on the top of frames might result in high losses, but is easy. Alternatively, placing them on bees decreases this loss and allows a reduction in the number of mites used. Introducing mites in cells is a highly controlled method that requires few mites, but it is tedious.

·   The rejection rate of mites by workers by grooming or hygienic behaviour.

·   The sterility of some mites.

·   The old age of mites of uncontrolled origin.

·   The availability of mites.

In general, the number of mites to be introduced in experimental colonies should be overestimated to guarantee a sufficient sample size.