Mixing up the gene pool

RALEIGH, N.C. -- Queen bees who cavort with multiple mates are not behaving badly.

Such procreative preferences help honeybee colonies survive by bringing more genetic diversity into the mix, according to a new study by entomology researchers at North Carolina State University and other institutions.

"High genetic diversity produces more eggs that resist disease better, and those colonies function more efficiently than less-diverse colonies do," says David Tarpy, an associate professor of entomology at NCSU and lead author of the research paper published in the German scientific journal Naturwissenschaften -- The Science of Nature.

Tarpy says the findings are part of a long-range study into potential causes of colony collapse disorder, a mysterious condition in which a colony's worker bees all disappear. The disorder was first identified in 2006, when some beekeepers reported losses of a third to 90 percent of their hives.

Numerous factors may adversely affect bee colonies, including pests such as the varroa mite, which feeds on bee larvae and pupae. Other potential problems for hives include certain types of bacteria, applications of pesticides or insufficient food supplies. When such problems arise, a diverse genetic mix could be a valuable asset for a colony.

"Mixing the genes in a given colony helps to hedge their bets, so if some members of the colony aren't doing so well, their half-sisters can take up the slack," says Don Hopkins, who oversees beekeeping operations for the North Carolina Department of Agriculture and Consumer Services.

While other research has focused directly on analyzing collapsed colonies, Tarpy and his colleagues looked at the genetic diversity of bees in hives in the spring and again at the end of the summer.

"We found that colonies with low levels of genetic diversity were more likely to die by the end of that period," Tarpy says.

He says the research findings don't fully explain mysterious colony collapse disorder, but "could be a piece of the puzzle."

By taking samples from 80 honeybee colonies and evaluating their genetic diversity, Tarpy and his colleagues -- Dennis vanEnglesdorp at the University of Maryland and Jeffery S. Pettis at the U.S. Department of Agriculture Bee Research Laboratory in Beltsville, Md. --determined that colonies whose queens had mated seven or more times were nearly three times more likely to survive to the end of the 10-month honeybee working season than those that mated fewer times.

Forty-eight percent of those colonies whose queens had seven or more mates survived. Fewer than 20 percent of the less genetically diverse colonies made it to the end of the 10-month period.

A single queen typically lays all the eggs for an individual hive, which can support as many as 80,000 bees, including male drones and infertile female worker bees, Hopkins says.

A newly emerged queen, known as a virgin queen, goes out on mating flights within days of becoming an adult bee.

"She flies from the hive to sow her wild oats, mating with drones from other colonies," Tarpy says.