No Single Villain Behind Honey-Bee Colony Collapse

By Susan Milius, for Science News' On the Scene Blog

INDIANAPOLIS, IND—Jeff Pettis continues to break the hearts of mystery lovers.

Two years ago he and other entomologists went to work on what sounded like the scenario for rip-roaring fiction: widespread, unexplained disappearances of honey bee workers that left the youngsters and queen behind for no obvious reason.

His progress report to the national meeting of the Entomological Society of America, however, isn’t pointing toward a fictional crescendo. Pettis argues that there may not be a Colonel Mustard in the kitchen with the candlestick, but a web of subtly interacting factors. At his presentation December 12, he might have been an epidemiologist chiding humans about the need for life style changes: … multiple stresses … subtle interactions … importance of nutrition.

Pettis is an entomologist though, the research leader at the USDA Agricultural Research Service’s Bee Research Laboratory in Beltsville, Md. For at least a year, he has been talking about the interaction hypothesis.

He points out that a working honey bee leads a tough life in today’s landscape of imported parasites and long-distance road trips to agricultural fields that may have low nutritional value but considerable pesticide residues. He proposes that such stresses weaken the bees and interact with other menaces, such as viruses, which can massacre a colony.

Other research, which he didn’t review, has identified viruses that lead bees to expire when they have ventured beyond their hives. That quirk might explain the syndrome’s illusion of vanishing workers.

As examples of worrisome stresses, Pettis described sublethal doses of pesticides, under study in cooperative research with Galen Dively of the University of Maryland in College Park. In this work, bees didn’t die from weeks of exposure to a neonicotinoid pesticide. But when the same bees faced a later challenge, the nasty fungal pathogen Nosema ceranae, they developed worrisome infections. Pesticide-exposed bees ended up with three to four times as many Nosema spores in their body as did bees without the pesticide preview. “It’s a very subtle interaction we wouldn’t have detected” without the specific test, Pettis said.

Hauling bees across the country adds more stress, although Pettis says he’s not betting that the long-standing problems of transportation will prove a major factor in the recent colony collapses. Nevertheless, ARS and other institutions are looking into the stress. A comparison of hives shipped away versus ones left in place found higher egg and larval losses in the transported colonies, he said.

Also, bees on the road failed to manage their hive temperature as well as the stationary ones do, Pettis said. Hives sitting in California stayed near 34 degrees Celsius even though day and night outdoor temperatures zigged and zagged during the same period. When traveling on a truck though, hive temperatures lost their relatively even control and began spiking and dipping.

This multiple-stress approach to the bee dilemma doesn’t grab public imagination the way a classic mystery villain does. Yet it’s just as worrisome. Adding colony collapse disorder to the other perils honeybees face has raised winter losses to around 30 percent, Pettis said. Beekeepers have divided hives and compensated to some extent so far, but “this is becoming unsustainable,” he said.

At one point in his talk, Pettis showed what might have been taken as a sign of stress himself under other circumstances. He volunteered that approaching the presentation room, he began to wonder whether he should have tied a large pink bow in his hair.

The audience merely nodded in understanding. The entomology meeting shared the convention center with the World Sprit Federation’s cheerleading competition. Reaching any scientific talk involved dodging through throngs of young girls in spangled outfits, face paint and big, glittering hair bows.

---

 Follow U.S. News Science on Twitter.