A parasitic mite has helped a virus wipe out billions of honeybees throughout the globe, say scientists.
A team studying honeybees in Hawaii found that the Varroa mite helped spread a particularly nasty strain of a disease called deformed wing virus.
The mites act as tiny incubators of one deadly form of the disease, and inject it directly into the bees’ blood.
This has led to “one of the most widely-distributed and contagious insect viruses on the planet”.
The findings are reported in the journal Science.
The team, led by Dr Stephen Martin from the University of Sheffield, studied the honeybees in Hawaii, where Varroa was accidentally brought from California just five years ago.
Crucially some Hawaiian islands have honeybee colonies that are still Varroa-free.
This provided the team with a unique natural laboratory; they could compare recently-infected colonies with those free from the parasite, and paint a biological picture of exactly how Varroa affected the bees.
The team spent two years monitoring colonies – screening Varroa-infected and uninfected bees to see what viruses lived in their bodies.
Dr Martin explained to BBC Nature that most viruses were not normally harmful to the bees, but the mite “selected” one lethal strain of one specific virus.
“In an infected bee there can be more viral particles than there are people on the planet,” Dr Martin explained.
“There’s a vast diversity of viral strains within a bee, and most of them are adapted to exist in their own little bit of the insect; they get on quite happily.”
But the mite, he explained, “shifts something”.
A pitched battle about why bee populations around the world are declining so rapidly has been joined by two new studies pointing directly at the harm from insecticides most commonly used by grain, cotton, bean and vegetable farmers.
Pesticides were an early suspect, but many additional factors appear to be at play — including a relatively new invasive mite that kills bees in their hives, loss of open land for foraging, and the stresses on honeybee colonies caused by moving them from site to site for agricultural pollinating.
The new bee research, some of the most extensive done involving complex field studies rather than simpler laboratory work, found that exposure to neonicotinoid pesticides did not kill the bees directly, but changed their behavior in harmful ways. In particular, the insecticide made the honeybees and bumblebees somewhat less able to forage for food and return with it to their hives.
While the authors of the studies published Thursday in the journal Science do not conclude that the pesticides are the sole cause of the American and international decline in bees or the more immediate and worrisome phenomenon known as colony collapse disorder, they say that the omnipresent chemicals have a clearly harmful effect on beehives.
Orkin, the pest control company, recently said its agents nationwide are reporting a 30 percent increase in calls to treat ant infestations compared with this time last year. Termite swarms do not normally show up until the end of March, but Orkin received 85 termite-control calls in February.
An Orkin branch in Montgomery County, which serves the District, has already responded to mosquito sightings this year. And the National Pest Management Association, based in Fairfax, issued an early warning of ticks, possibly carrying Lyme disease, lurking in back yards.
County agricultural extension agents across the country are sending out bug alerts to farmers.
“These things are coldblooded,” said Mike Raupp, a professor of entomology at the University of Maryland. “Whenever we have a warm winter, they’re going to be out earlier. How do you stop them? You pray for cold weather.”
A mild winter is not great for all bugs, including some highly beneficial insects. Some were up and about when they should have been idle and hibernating, burning less energy, experts say. When this happens, they gobble the food they stored for the winter and emerge into a world where food is scarce. Many starve.
By Glenn I. Teves, County Extension Agent, UH CTAHR Cooperative Extension Service
The relationship between humans and honeybees is ancient, as demonstrated by cave paintings in Spain, South Africa, and Nepal, depicting honey hunters collecting honey from wild hives. The honeybee was introduced to Hawaii in 1857, but the accidental introduction of the Varroa mite in 2007 puts this relationship in jeopardy and is one example of Hawaii’s vulnerability to invasive species.
The Varroa mite (Varroa destructor) is one of the most serious pests of honeybees and is associated with the spread of viruses and the decline of honey bee colonies on the mainland. And it’s only a matter of time before it destroys all feral honeybee colonies in Hawaii. On the island of Oahu alone, over 90 percent of the wild colonies have been wiped out and it has now moved to the Big Island, starting in Hilo. Visual checks of feral honeybees in Ho`olehua and Mo`omomi have not found the Varroa mite to date.
The mites attack both adult bees, and also larvae in the hive. Although honeybees in Hawaii are crosses between German, Italian, and Carnolian bees, the honeybees on Molokai appear to be a special disease resistant strain, first brought in around 1898. They show resistance to a disease called Foul Brood, which wiped out honeybees on most of the islands starting in 1908.
HILO — In just over a year’s time, the varroa mite, a parasite that kills honeybees, has spread from the Hilo Bay area north to Onomea and south to Pahala, researchers say.
And it is not a matter of if, but when, the mites will spread to West Hawaii, said Ethel Villalobos, an entomologist at the University of Hawaii’s College of Tropical Agriculture and Human Resources.
Although it isn’t known how quickly it will happen, Villalobos said it will because bees are naturally on the move seeking sources of pollen, and farmers and beekeepers often move hives, and can unknowingly move a colony infested with parasite.
"The bottom line is: Varroa mites have been all over the world and the mainland for the last 20 years, and it’s substantially changed the way agriculture is done on the mainland. It will substantially change the way we do agriculture here," said Richard Johnson, owner of Onomea Orchards and president of the Hawaii Tropical Fruit Growers.
"It’s not the end of agriculture," he said. "It wasn’t on the mainland. We’re going to have to learn to live with it, we’re not going to eliminate the varroa mite. … It’s going to become an art of living with varroa."