Pest description A common cleptoparasitic mite (males: 0.45 mm, females: 0.60 mm) that appear white and ovoid and reproduce rapidly. Female mites lay eggs in BOB cells. Immature mites feed on the pollen grains of the provisions. Eggs may be punctured by mites or young larvae may starve. Typically mites cannot move between cell partitions unless mud partitions are damaged or cracked. Thousands of mites may inhabit infested cells by the end of the summer. Phoretic nymphal mites cling to bee hairs and spread to other nest cavities. The mites physically hinder the flight of bees. Non-phoretic mites remain in the cavity where they hatch and reproduce.
Management Mites exhibit susceptibility to dehydration in the early stages of their lives. To control, use porous nesting materials and wood or paper inserts. Nest boxes may be taken down early. Incubate the larval nests in the nest box under warm and dry conditions, around 85°F for several weeks to months. Check the nests periodically for mature adults. If using straw inserts, examine whole nests by splitting the straws lengthwise. Remove remaining mite-infested cells. When all bees have reached maturity, they may be moved outdoors temporarily (a few days) and subsequently moved into the refrigerator for overwinter storage. Chaetodactylus krombeini mites infesting horn-faced bees (Osmia cornifrons) have been controlled using formic acid and wintergreen oil fumigants. If this technique is used, care should be taken due to the potential of killing the BOB.
For more information:
Sugden, E. 2001. Mitey bees: the blue orchard bee's mite pest (http://crawford.tardigrade.net/bugs/BugofMonth35.html)