Every year, up to half the honeybee colonies in the U.S. die. Varroa mites, the bees’ ghastly parasites, are one of the main culprits. After hitching a ride into a hive, a mite mom hides in a honeycomb cell, where she and her offspring feed on a growing bee. But beekeepers and scientists are helping honeybees fight back.
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Photo of varroa mite: D. Kucharski K. Kucharska/Shutterstock.com
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To feed, a varroa mite nestles between a honeybee’s protective plates. It digs in with its gnarly mouth, the gnathosoma. The mite sinks it into a crucial organ called the fat body, a layer of tissue that lines the bee’s abdomen.
Sort of like the human liver, the fat body helps the bee break down harmful stuff, including pesticides. And it maintains the bee’s immune system. So, when varroa mites attack the fat body, they seriously weaken the bee.
The mites can also transmit a virus that causes a bee to be born with deformed wings, no good for flying.
--- Where do varroa mites come from?
Varroa mites evolved on eastern honeybees in Asia, known by the scientific name Apis cerana. Only recently have the mites moved onto western honeybees (Apis mellifera), the species that beekeepers maintain in the Americas, Europe and Africa. Varroa mites were first seen in the U.S. in the 1980s. They are now a pest of western honeybees around the world.
--- How do you get rid of varroa mites?
Beekeepers monitor the number of varroa mites in their hives throughout the year. One test they perform is called the “sugar shake.” The test consists of measuring a half-cup of bees (about 300), putting them in a mesh-covered jar, adding 2 tablespoons of confectioners’ sugar, and shaking for about 30 seconds. This causes the mites to lose their grip on the bees. The beekeepers then empty the sugar onto a tray and count the number of mites that fell through the mesh. A varroa mite infestation that represents between 1% and 3% of bees in a hive is enough to prompt beekeepers to apply pesticides to kill the mites, says associate professor of cooperative extension in apiculture Elina L. Niño, who trains beekeepers at the University of California, Davis.
An effort is underway to keep mites at bay by selectively breeding honeybees that can fight back. Scientists at the U.S. Department of Agriculture and private companies like VP Queen Bees in South Carolina are breeding bees that can sniff out varroa mites and uncap the cells they’re in before they can reproduce. This bee behavior is called varroa sensitive hygiene.
At Purdue and Central State universities, researchers are using a different approach, breeding bees known as “mite-biters” or “ankle-biters” for their ability to kill varroa mites by chewing off their legs.
---+ Find additional resources and a transcript on KQED Science:
https://www.kqed.org/science/1984850/varroa-mites-are-a-honeybees-8-legged-nightmare
---+ More great Deep Look episodes:
Honey Bees Make Honey … and Bread?
https://youtu.be/sAKkjD3nEv0?si=jz4FVmJElA_jip-P
Busy Bees and Other Pollinators Playlist
https://youtube.com/playlist?list=PLdKlciEDdCQCfoI8E24mbuk259unmiwG9&si=lprbSmYhVhcc_Tnk
---+ GIF CHALLENGE Shoutout!
It was a tough question in our YouTube Community Tab GIF challenge! The organ the mites feed on is the "fat body," and its closest analog in humans in the liver. One fan got the question partially right, by answering "liver:"
@bssn9469
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