WASHINGTON, Nov. 16, 2015 - U.S. honey bee colonies could be in for a bad winter.

That’s the word from Dick Rogers, the principal scientist with the Bayer Bee Care Center in North Carolina, who’s been studying honey bees for decades. In a blog post, Rogers says he conducts hive evaluations during late summer and early fall, often involving up to 150 samples from hives across the country, and this year he’s alarmed by the prevalence of a hive parasite called the Varroa mite.

Rogers found through his research that a hive containing three Varroa mites for every 100 bees can mean serious trouble for a honey bee colony. That fraction may not seem significant, Rogers says, but a typical colony may contain 40,000 bees – and that equates to more than a thousand parasites, which weaken bees through their feeding and disease transmission activities.

“This year I’m finding at least two-thirds of the hives I’ve examined contain mite counts above that threshold and many have exceeded seven mites per 100 bees, a level that is almost certain to result in colony failure this winter,” he writes.

Recent presentations at several scientific conferences indicate that two organizations – the Bee Informed Partnership and USDA – are estimating infestation levels between seven and eight mites per 100 bees as a national average this fall, he said.

Why should we care? According to USDA, bee pollination is crucial to U.S. agriculture, responsible for more than $15 billion in increased crop value each year. About one mouthful in three in our diet directly or indirectly benefits from honey bee pollination, the department says on its website, and commercial production of many specialty crops – like almonds and other tree nuts, berries, fruits and vegetables – depend on pollination by honey bees.

The Varroa mite is one of several possible factors that scientists blame for Colony Collapse Disorder, a phenomenon that began about a decade ago in which overwintering honey bee populations experienced dramatic die-offs. Other possible factors include the increased use of potentially toxic insecticides, called neonicotinoids, as well as habitat loss. From 2006 through 2011, about a third of U.S. honey bee colonies were lost each year, USDA says, with a third of these losses attributed to CCD by beekeepers. The winter of 2011-2012 was an exception, when total losses dropped to 22 percent.

In his blog, Rogers notes that since 2013, U.S. beekeepers have been doing better at reducing winter honey bee colony losses, and he attributes part of that to better management of the Varroa mite. Rogers’ research also suggests the most effective treatment against Varroa infestation, a pesticide called Apivar, may be losing its efficacy, however.

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“Since there are few effective treatments for Varroa and these mites are prone to develop resistance, the potential loss of this acaricide (a substance poisonous to mites or ticks) from our management toolbox is very concerning,” Rogers writes. 

While scientists are testing new pesticides and looking to improve honey bee genetics to increase the bee’s tolerance to the Varroa parasite, “for now, there is little beekeepers can do to change the hand they’ve been dealt.”

“Winter normally is a stressful time for colonies, but high mite infestations make this year’s situation particularly challenging and I am expecting the worst,” he says, adding, “I hope I’m wrong about the consequences associated with the levels of Varroa we’re seeing.”


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