# 4.5.2.1. 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.