Bees May Accidentally Bring Varroa Mites Into Their Hives

Bees May Accidentally Bring Varroa Mites Into Their Hives

Varroa mites, like the one attached to the back of this honey bee, can decimate unprotected hives. The tiny parasites feed on the bees' blood and can infect them with harmful viruses. (Photo credit: Scott Bauer, USDA-ARS)

Varroa mites, like the one attached to the back of this honey bee, can decimate unprotected hives. The tiny parasites feed on the bees’ blood and can infect them with harmful viruses. (Photo credit: Scott Bauer, USDA-ARS)

USDA researchers are studying closely the behavior of honeybees, not just to learn about how they behave but also how Varroa mites interact with the bees.

Agricultural Research Service (ARS) Supervisory Research Entomologist Gloria DeGrandi-Hoffman is leading a team of researchers studying entrances of victimized hives, eyeing the comings and goings of foraging honeybees that may be a vector for the Varroa mite.

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The team blockings access (something missing here?) to the hives using cut lengths of PVC pipe with a slit about midway down. There, a sliding wire-mesh door separates incoming bees from outgoing ones.

The team’s investigations in Bismarck, ND, this June are actually a follow-up study to the one they completed last year at two Arizona sites. Findings from that study suggest that bees can bolster their hives’ existing mite population by carrying in Varroas from other colonies, an influx that most often occurs in the fall, especially November.

Varroa populations grow slowly because females produce only three to five offspring. If mite populations in colonies are low, then they should remain that way for at least a season before miticides need to be applied, explains DeGrandi-Hoffman, who leads ARS’s Carl Hayden Bee Research Center in Tucson, AZ.

Sometimes, though, Varroa numbers soar to potentially hive-wrecking levels during the fall. To the researchers, this suggested that factors other than mite reproduction were involved-namely, mite migration via foraging bees and wayward “drifters” from other colonies. At the Arizona hive sites, this influx of migrating mites correlated to population increases of 227% to 336%, starting in November. The findings appeared in the February 2016 issue of Experimental and Applied Acarology.

In addition to further investigation at a Bismarck apiary, the researchers will also evaluate placing hives in refrigerated storage in the fall to head off mite migration into colonies. They’ll determine the strategy’s effectiveness based on whether it reduces the need for miticide applications, keeps Varroa populations low, and results in high winter survival rates for colony members.