Biology and Effects to Colonies
Most bee colonies in North America and Europe are infested with varroa (Varroa jacobsoni). Female varroa spread easily among colonies on drifting bees. Mites select brood cells that are soon to be capped in which to rear their young. Both the mother and her young feed on the blood (haemolymph) of developing honey bee pupa. When the adult bee emerges so do all female varroa offspring that have completed development. The mites stay attached to adult bees until they are prepared to infest new brood cells. In this way varroa populations rise steadily during the brood rearing periods of spring and summer. Peak varroa populations in late summer and early fall, if left untreated, result in colony collapse.
Varroa feeding results in honey bee pupa that emerged undernourished and often with deformed shrivelled wings. Pupae fed on by varroa develop into adults that have severely reduced lifespans and are less able to perform essential colony tasks such as nursing and foraging. Widespread parasitism results in colony collapse, usually by late summer or early fall.
Varroa mites severely impact normal colony functions resulting in poor colony productivity prior to colony collapse. Alternate hard chemicals and natural acids for control of varroa.
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Varroa entering brood cell |
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Varroa entering brood cell |
Diagnosis
Mature female varroa mites are pinhead-sized and reddish brown. Mites can be found:
- Attached to adult bees on the top of the thorax or on the underside of the abdomen.
- Within sealed brood cells (particularly in drone brood).
Several methods are available for monitoring colonies for varroa levels in colonies. The most widely accepted and researched method involves counting the number of mites falling onto a screened sticky surface on the colony bottom board. A mite strip can be used in conjunction with bottom board varroa mite drop, providing a much more sensitive measurement.
Colony monitoring can help beekeepers determine:
- Is treatment for varroa necessary?
- Did the treatment work?
Treatment
More Information