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With parasitic mites in ascendance, honeybee losses reach a grim new high

Honeybees
REUTERS/Fabrizio Bensch
A fresh survey shows that honeybee colony losses last winter set a high at 37.7 percent — an increase of 7 percentage points above the previous year.

The declining fortunes of America’s honeybees, and their keepers, appear to have taken another big dip.

A fresh survey shows that colony losses last winter set a high at 37.7 percent — an increase of 7 percentage points above the previous year, and nearly 9 points above the average established since data-gathering began 13 years ago, with the emergence of colony collapse disorder.

Full-year losses were high, too, at 40.7 percent, but that was only slightly worse than the previous year and not quite three points above the 13-year average. Annual losses reached 45 percent in 2012-13, and were almost as bad in three of the intervening years.

While full-year losses may seem like the more important figure, reflecting total annual damage to managed honeybee colonies and the costs to their keepers, the winter rates are of greater concern because they are considered a more reliable measure of the bees’ baseline health.


Because bees are in a state of semi-hibernation for much of the period from October through March, their exposure to pesticides is significantly lessened, as is their need for the healthy forage habitat whose availability just keeps contracting.

But the clear indication in this year’s data is that a third major stressor may be coming to the fore: the parasitic affliction of varroa mites and the suite of ever-evolving viruses they carry. Also, apparently, declining effectiveness of the miticides beekeepers have been using to defend their hives.

One telling statistic on that point is that over-winter loss rates were virtually identical across the three types of beekeeper participating in the Bee Informed Partnership survey: the “backyard beekeepers” who keep 50 hives or fewer, the large-scale commercial beekeepers who manage more than 500, and the “sideline” operators in between.

In past years, the commercial operators have generally done better in limiting winter losses, presumably because of their greater investment, and expertise, in mite control. Last winter, however, their loss rate of 37.5 percent was better than the backyarders’ (39.8 percent) but worse than the sideliners’ (36.5 percent).

All three sectors had losses far above what survey respondents termed an “acceptable” loss rate of 22.2 percent. (That figure also ticked up a couple of percentage points from last year, the partnership said, perhaps reflecting a firmer grip on the fix they’re in.)

Threat to bees and keepers

In an announcement of the findings from the University of Maryland, where the Bee Informed program is based, entomologist and partnership president Dennis vanEngelsdorp called the latest results “very concerning” and emphasized the parasite factor:

We are increasingly concerned about varroa mites and the viruses they spread. Last year, many beekeepers reported poor treatment efficacy, and limited field tests showed that products that once removed 90% of mites or more are now removing far fewer. Since these products are no longer working as well, the mite problem seems to be getting worse.


But mites are not the only problem. Land use changes have led to a lack of nutrition-rich pollen sources for bees, causing poor nutrition. Pesticide exposures, environmental factors, and beekeeping practices all play some role as well.

In all, vanEngelsdorp called the loss figures “very concerning” and not only because of the ongoing threat to honeybee populations. “We’re not really worried about honeybees going extinct,” he said. “I’m more worried that the commercial beekeepers will go out of business.”

Either development, of course, would have significant ramifications for the $15 billion in U.S. annual food production that relies on pollination, principally from honeybees  and for the diets of Americans who might like to have melons and blueberries alongside the corn and soybean products.

VanEngelsdorp’s colleague Karen Rennich, the partnership’s executive director, added:

The tools that used to work for beekeepers seem to be failing…. A persistent worry among beekeepers nationwide is that there are fewer and fewer favorable places for bees to land, and that is putting increased pressure on beekeepers who are already stretched to their limits to keep their bees alive.

We also think that extreme weather conditions we have seen this past year demand investigation, such as wildfires that ravage the landscape and remove already limited forage, and floods that destroy crops causing losses for the farmer, for the beekeeper, and for the public.

There is no such thing as perfect winter weather for bees, according to the partnership. If it’s too cold, it can be difficult to keep the hives supplied with food; if it’s too warm, it strengthens the mites and their attacks on the hives.

Minnesota in prime forage zone

Prime overwintering ground for managed honeybees, by the way, is right here in Minnesota and other portions of the “prairie pothole” region that stretches from Alberta down through central Iowa. The declining availability of good honeybee forage in that broad swath is the focus of another new research effort, which finds that on a global basis, habitat loss is an even more significant driver of insect die-offs and extinctions than pesticides and other “agrochemical pollution.”


The U.S. portion of the region provides spring and summer foraging ground for nearly 40 percent of the nation’s commercially managed bees, according to a paper published in the journal Land Use Policy, and this in turn directly influences their chances of over-winter survival. Alas, the future for this happy picture is somewhat clouded:

One of the reasons the PPR is a keystone for wildlife and beekeeper livelihood is the existence of the [Conservation Reserve Program], a voluntary program administered through the Farm Service Agency under the United States Department of Agriculture (USDA). Established in the 1985 Farm Bill, the CRP pays an annual rental fee to landowners to remove marginal farmland from crop production for the establishment of perennial cover, typically in the form of a grassland.

As of 2018, around 22.7 million acres of land were enrolled in the CRP nationwide, with a designated funding of $2 billion annually. The benefits of CRP land include improved soil health, wildlife habitat, water quality, and carbon sequestration.

The CRP has also helped maintain forage sites for commercial beekeepers, who largely do not own the land they need for honey production, but rather, rely almost entirely on contractual arrangements with landowner. CRP land is attractive to beekeepers for honey production partly because landowners are restricted in their ability to hay and graze the land, so beneficial flowering plants can bloom and provide nutritious resources to bees throughout the growing season.

However, the convergence of cuts in CRP funding with surging production of corn and soybeans — partly in response to world grain prices, partly because of biofuels production — is causing a rapid reversal of the setasides.

Among the states encompassing the PPR, 4.9 million hectares (12.2 million acres) were enrolled in the CRP in 2007, but by 2017, enrolled acreage had declined by nearly half to 2.7 hectares (6.8 million acres). Notably, the highest rate of grassland conversion to cropland in the PPR took place in areas within 100 miles of corn ethanol refineries from 2008 to 2012.

Conversion of grassland to corn or soybeans in the PPR replaces valuable bee forage and habitat with monoculture crops that have little nutritional value to bees, thereby reducing forage quality of the landscape. Although CRP land has diminished  throughout the U.S., some of the most drastic losses have been in the PPR, in close proximity to prime beekeeping areas.

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The Bee Informed Partnership report is here; the paper in Land Use Policy, “Feeling the sting? Addressing land-use changes can mitigate bee declines,” can be found here but access is not free.

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Comments (2)

  1. Submitted by Richard O'Neil on 06/27/2019 - 02:34 pm.

    All the news about bees is bad news… and never any good news. Depressing!

  2. Submitted by William Hunter Duncan on 06/28/2019 - 12:23 pm.

    Extermination of pollinators, polluted waters, soil loss, destruction of local economics and the communities that depend on that, ever greater income inequality, global overpopulation and all the ecological pressure inevitable then.

    Feeding the world, the mantra of big ag, has a bit of a different ring to it, when you strip it of it’s marketing veneer. Destroying the land and waters and the local here, to make a few executives and shareholders rich, more like it.

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