Glossary
The quantitative measurement of varroa mite (Varroa destructor) infestation levels in a honey bee colony, expressed as the number of mites per 100 bees (percent infestation). Regular mite monitoring is the cornerstone of modern integrated pest management in beekeeping and determines when treatment is necessary.
Varroa mites are the single greatest threat to honey bee colony survival worldwide. Every colony in North America is infested with varroa; the question is not whether mites are present, but how many. Low mite levels (below 2 percent) can be tolerated by strong colonies, but levels above 3 percent during the active season or above 2 percent in fall indicate treatment is urgently needed.
Without monitoring, mite populations grow exponentially and reach lethal levels by fall, producing a generation of virus-laden winter bees too weakened to sustain the colony through cold months. This mite bomb effect is the leading cause of winter colony losses, and it is entirely preventable with regular monitoring and timely treatment.
The two most common monitoring methods are the alcohol wash and the sugar roll. Both involve collecting approximately 300 bees (half a cup) from a brood frame, gently dislodging mites from the bees, and counting the mites that fall off. The alcohol wash (using rubbing alcohol) is more accurate but kills the sample bees. The sugar roll (coating bees in powdered sugar) is slightly less accurate but allows the bees to be returned alive.
Many beekeeping experts recommend monitoring mite levels at least monthly from April through October. A sudden spike in mite count between monitoring sessions indicates rapid population growth and the need for immediate treatment.
A threshold of 3 mites per 100 bees (3 percent) during spring and summer, or 2 mites per 100 bees (2 percent) in fall, is widely used as the treatment threshold. Some beekeepers set even lower thresholds. Any count above these levels should trigger treatment planning.
Collect approximately 300 bees (half a cup) from a brood frame into a jar with a screened lid. Add 2 tablespoons of powdered sugar, roll gently for 1 minute, and shake the sugar through the screen onto a white surface. Count the dislodged mites in the sugar. Divide by 3 to get approximate mites per 100 bees.
Monthly monitoring from April through October is recommended as a minimum. Critical monitoring periods are spring (April-May), mid-summer (July), and pre-treatment assessment in late summer (August-September). Fall counts after treatment verify treatment effectiveness.
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