Mites are pests for mason bees. Bees carry them from their old nest to their new nests, and then mites compete for food with the young developing bees. Mostly, if mites get into a cell with a developing bee and its pollen lump, mites will be the end result- not a bee.
Because mites on the surface of cocoons are waiting to be transported to a new nest by the emerging bee, it is imperative to get rid of most, if not all surface mites. Washing will remove the majority or mites. Rolling cocoons over a metal screen will remove the majority of the remaining mites.
Further reading on mite control ______________
A great DVD on How to _________________
Here are a few pictures of
Mites are transported by bees from the old nest to the new.