Honey bees are apparently the Typhoid Marys of the pollinator world. A study suggests that honey bees spread two kinds of pathogens to wild bumblebees. And one of these, deformed wing virus (DWV), is killing bumblebees across the United Kingdom, perhaps contributing to the decline of the nation’s wild populations. The wide occurrence of DWV is “truly alarming,” says molecular ecologist Peter Neumann of the University of Bern, who was not involved in the study.
DWV can be nasty. Like many other viruses in honey bees, DWV spreads in two ways. Worker honey bees (Apis mellifera) will transmit it orally to other workers, generally resulting in a benign infection. But the parasitic varroa mite is a carrier, too. When the mite feeds on bee pupae, infecting them with DWV, the virus causes ghastly deformities. Young bees develop with bloated abdomens and shrunken or crumpled wings, making DWV one of the worst viral diseases in commercial honey bee hives.
DWV first turned up in 2004 among commercial bumblebees; the insect, Bombus terrestris, is often used in greenhouses, particularly to pollinate tomatoes. Commercial breeders initially noticed that about 10% of their bumblebee queens had died with tiny, misshapen wings. Then, Elke Genersch of the Institute for Bee Research in Hohen Neuendorf, Germany, and colleagues discovered that the dead bumblebees had been infected with DWV. The researchers suspected that honey bees had orally infected the bumblebees, because breeders use honey bees to encourage bumblebee queens to start new nests.
No one knew the extent of DWV in wild bumblebees. Matthias Fürst and Mark Brown of Royal Holloway, University of London, in Egham and colleagues collected honey bees and bumblebees from 26 sites across Great Britain. The virus was present in 11% of the bumblebees and replicating in more than a third of those, suggesting active infections, they report in Nature. The virus is probably even more common than those data indicate, Brown noted in a telephone press conference. Bees “on their deathbed are not going to be caught by our sampling scheme,” he said.
The team found genetic evidence that the virus is shared between the species: When honey bees and bumblebees lived near each other, both had a similar strain of the virus. Because DWV was more prevalent in honey bees—36% were infected—the researchers believe it spreads from them to bumblebees. The team also found the same pattern with the fungal pathogen Nosema ceranae, but it did not appear to cause problems for bumblebees.
DWV, on the other hand, spelled trouble. When the researchers fed bumblebees food contaminated with the virus, symptoms of the disease emerged. (See photos of bumblebees with deformed wings, not from this study.) Worker bees became sick and died on average 6 days sooner than normal, a major reduction from the typical lifespan of 21 days. A bumblebee nest contains fewer than several hundred worker bees, so any widespread DWV infection could devastate the nest’s ability to gather enough food.
Jeff Pettis of the U.S. Department of Agriculture Bee Research Laboratory in Beltsville, Maryland, agrees it is likely that honey bees are infecting bumblebees. “This highlights the need to better manage honey bees in a responsible manner and find ways to conserve all pollinators,” he says. Wild bumblebee populations, which help pollinate some field crops, appear to be declining in many places, so the need is urgent. There is no way to treat sick bees, so the best strategy is to keep honey bee hives as healthy as possible, in particular by controlling the varroa mites, which worsen infections in honey bees.