Health of Honeybees Tied to Genetic Trait
John Davis is pleased as he inspects one of his hives for signs of a parasite that can wreak havoc on honeybees. “I can’t find a single mite today to save my neck, and that’s a good thing,” said the retired paper-manufacturing supervisor. He started beekeeping at age 15 when his biology teacher, who was a beekeeper, talked about bee research. Davis and his wife live in Powhatan County, where he has 40 hives. He is a master beekeeper, certified by the Virginia Beekeepers Association, and quite knowledgeable of bee history.
Davis said many people don’t know that honeybees are not native to North America. Early European settlers brought hives of bees to the New World on ships. “Native Americans called them white man’s flies,” he noted.
Davis is on a mission to help beekeepers control the leading cause of colony collapse. Colony collapse happens when most of the worker bees disappear, leaving behind only the queen and a few other bees to care for her. “It’s a scientific, controlled approach to something that can’t be controlled,” he said, noting that bees can’t be contained in a lab and expected to do their jobs, including mating, pollination and making honey. “The normal attrition rate for bees is about 10 percent, but with colony collapse it has reached as high as 70 to 80 percent,” Davis said. Controlling colony collapse is critical since honeybees are essential crop pollinators.
A popular theory is that colony collapse is caused by pesticides. Davis said that pesticides could be a contributing factor but not the major cause. However, he emphasized, it is important to use pesticides carefully and according to directions, especially near bee hives or where bees forage. Davis said that the major cause of colony collapse is the varroa mite, an external parasite that attaches to honeybees. The mites suck blood from the bees, which weakens the bees and shortens their lifespans.
Davis participates in a U.S. Department of Agriculture (USDA) program to help control the mites by cross-breeding bees that have an inheritable genetic trait called varroa sensitive hygiene (VSH). Bees with this trait are resistant to varroa mites and also detect and remove varroa-infested larvae from the colony before they become adults. Davis is concentrating on selective breeding of queen bees with VSH traits that can be passed along during mating.
Each beehive contains one colony, or family, of bees. Each colony has only one queen. Normally when a queen dies or disappears from the colony, worker bees in the colony follow their normal instincts and select a new queen-to-be from other worker bees in the larval stage. The workers place the larva in a special queen cell in the honeycomb and feed it only royal jelly, a substance secreted by worker bees, causing the larva to develop into a queen.
Davis helps the natural process along to assure that new queens will have the VHS trait. He removes fully developed queens from colonies. He then selects larvae that have hatched from the eggs of queens known to have the desirable trait and places the larvae in queen cells. The worker bees then nourish the larvae into queens.
Davis sells queens with the VHS trait to other area beekeepers, thereby spreading the desirable trait. He also buys varroa-resistant queens from breeders who are certified by the USDA. “As long as I make enough to cover my expenses, I’m happy. I make a lot more on bees than I do honey,” Davis said.
Another way to control varroa mite infestation is to remove any part of a hive that is seriously infested. Several natural chemical treatments are available, Davis said. Sprinkling ordinary powdered sugar in the hives coats the bees and causes the mites to fall off. This is a labor-intensive process because the sugar must be applied weekly.
Thymol, a chemical sold as an herbal supplement, is another treatment. It is the main component in the oil of the thyme herb. Oxalic acid and formic acid are used to treat the mites. Oxalic acid occurs naturally in many plants and is a food supplement as well as a wood bleach. Formic acid is in the venom of stinging ants and bees. It is used as a preservative and as an antimicrobial agent. Commercial pesticides, which Davis calls “hard chemicals,” also can be used.