Deb Brandt-Buehler
June 28, 2011

Varroa Mite on honey bee

Photo Courtesy of Scott Bauer/USDA Agricultural Research Service/Forestry Images

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Here, a varroa mite is on the back of a honey bee.

In the 1940s, researchers working to solve the health challenges of American foulbrood in honeybees found that these amazing creatures can smell diseases in their own developing brood. Hives practicing good hygiene can detect and clean out unhealthy brood-keeping disease from spreading further.

Building on this knowledge, Jeff Harris, a research entomologist at the USDA, ARS Honey Bee Breeding, Genetics and Physiology Research Lab in Baton Rouge, La., has been charged with breeding bees to be resistant to varroa mites.

“It turns out that when you produce bees that are good at keeping out American foulbrood or Chalkbrood, they are also fairly good at removing varroa mites from their hives,” Harris explains.

Breeding bees is a slow process. Since only one generation of bees can be developed in a year’s time, it can take a few years to achieve resistance and then determine how the bees are resistant. Harris has been able to identify honeybees that are capable of the hygiene to eliminate Varroa in developing cells. Called Varroa Sensitive Hygiene, or VSH bees, the animals exhibit nest-cleaning behaviors that are good for their colony.

Varroa Mite Development

Varroa mites are tiny, fast-moving parasites capable of attaching themselves to both the adult and developing honeybee. The adult-female varroa lays her eggs in brood cells leaving offspring to feed on the developing bee pupa. The result is baby bees that are underweight and weakened enough to be more susceptible to the spread of viruses.

The bees that Harris has been producing smell the mites inside the brood cells and kill off the offspring to keep the mites from exploding inside the colony.

Further Investigation

While Harris has been at work breeding for VSH, Dr. Greg Hunt, a bee specialist at Purdue University in West Lafayette, Ind., has been genetically selecting bees for increased grooming behavior.

“We are selecting for increased grooming behavior by looking at the proportion of chewed mites that fall from bees,” Hunt said. “We have developed a lab assay that correlates with the chewed mite results.” Hunt has unpublished data reflecting his ability to map chromosomal regions that influence bee grooming behavior.

“Greg’s expertise is looking for the markers in bees I produced,” Harris explains. A process that took 4 to 6 months of field testing has been reduced to hours in terms of identifying the most desirable VSH queens.

Fielding Better Bees

Dave Shenefield, owner of Clover Blossom Honey has a Specialty Crop Grant from the Indiana State Department of Agriculture to make more mite-tolerant, hardy queens available in Indiana.

Through the grant he is teaching beekeepers how to raise their own queens and select for resistance. Shenefield received two artificial-insemination devices so that he can work with survivor stock from different bee breeders. The use of stock from different breeders enables his project to maintain a high level of diversity while reducing the risk of inbreeding.

“I’ve been working with Dr. Hunt on the development of mite-resistant stock for about 20 years,” Shenefield says. “I felt it was a must for Indiana to develop its own queen project, where we get genetically diverse stocks and propagate them throughout the state to hopefully help sustain beekeeping in Indiana.”

According to Shenefield, the plight of honeybees has brought a lot of new people to the hobby. People are interested and want to help and get involved by learning to keep bees and establishing their own hives.

Through his grant, Shenefield is bringing diversity to the Indiana bees and while teaching new beekeepers how to develop their own mite-resistant hives. He’s also teaching about integrated pest management — nonchemical approaches to treating for mites.

“My personal opinion is that hobbyists don’t have to use chemicals to control mites,” Harris added. “Glenn Apiaries, in [Fallbrook] California, has experts and is the largest seller of breeder queens. Purebred VSH breeders are being crossed with non-VSH drones to create outcrop VSH bees. The outcrop VSH bees prevent the potential for inbreeding among the VSH lines.”

Purchasing VSH outcrop bees enables hobby beekeepers to maintain chemical-free hives. Without the chemicals, hobby beekeepers can avoid all concerns about contamination of comb, wax and honey.

But, Shenefield says, “A queen that’s mated in your own bee yard is probably the best queen to have.”

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