NC State researcher says bee colonies are healthier when queens take many mates

relder@newsobserver.comJune 17, 2013 

The queen bee has been numbered to allow researchers to follow her as she mates and lays eggs, some of which were examined to determine paternity.

DAVID TARPY

— Queen bees who cavort with multiple mates are not behaving badly.

In fact, such procreative preferences actually help honeybee colonies survive by bringing more genetic diversity into the mix, according to a new study by entomology researchers at N.C. 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,” said David Tarpy, NCSU associate professor of entomology and lead author of the research paper published this month in the scientific journal “Naturwissenschaften,” based in Germany.

Tarpy said 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.

While losses have not been as large recently in North Carolina, the condition still occurs here, said Don Hopkins, who oversees beekeeping operations for the N.C. Department of Agriculture and Consumer Services.

“The concern among beekeepers is just as strong as it ever has been,” Hopkins said.

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 arrive, 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,” Hopkins said.

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 said.

He said 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 USDA 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 who mated fewer times.

About half – 48 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 said. 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 said.

Each queen makes at least one and sometimes four or five trips from the hive during a period of about a week, staying out for a few hours each time and mating with one or more drones per trip.

The queen flies to areas where male bees gather, and finds suitors strong enough to fly alongside her as they mate in the air. After mating, the drone will die, because the males’ sex organs and part of its abdomen are torn away at the conclusion of the act.

This leaves the queen ready to receive a new mate – and a new set of genetic material – with each coupling.

Some queens conclude their mating ritual after mating a half-dozen or fewer times, while others mate with 30 or more drones. Then the queen returns to the hive to lay eggs. She never mates again, but continues to lay the fertilized eggs she has stored in her body to produce workers or queen bees. Drones develop from nonfertilized eggs.

Tarpy said the research study was also significant because it examined bees in as natural a setting as possible.

The colonies examined are those transported to farms and agricultural settings on a regular schedule to pollinate crops along the East Coast.

“These were real-world pollinators, the ones responsible for putting food on our tables,” Tarpy said.

Elder: 919-829-4528

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