The Why Files The Why Files --

Pollinators in peril

Meeting highlights pollinator peril

Bees: Some people love them. Some people hate them. But many crops and wild plants need them for pollination. And bees are suffering.

Since 2006, about one-third of American honeybee colonies have died each winter.

The queen survives, with a small coterie of helpers, but there's no evidence of robber bees or other pests.

Tens of thousands of worker bees are absent, having died outside the hive. That's colony collapse disorder, and CCD is a threat to people who like to eat a disturbing variety of foods.

Beekeepers don't count bees; they count colonies, which the rest of us call hives. And as the total number of colonies continues to decline, farmers are starting to worry about failures of key crops that are partly or wholly reliant on insect pollination.

California, with its massive and diverse agriculture, is ground zero for pollinator problems: the state's 700,000 acre almond crop attracts essentially every mobile bee colony in the country. Hives from Australia even visit for the brief, frantic pollination season.

Large flatbed truck carrying several dozen stacks of bee hives and forklift on dirt farm road
A truck load of bees "commuting" to their job site. Long-distance travel can mix pests and diseases. Does it contribute to colony collapse?

The price to rent a colony in California has about doubled in the past couple of years -- one indication of the growing honeybee scarcity.

Bees on the move

Honeybees were imported to the United States about 400 years ago to provide wax, and then honey and pollination, but almost 4,000 native bee species are also on the job in this country alone. Unlike honeybees, the natives generally nest in the soil and live alone or in small groups, and unlike honeybees, cannot support "by the truckload" pollination services.

Beekeeping has evolved from a backyard pursuit where the main benefit was honey into a transcontinental business: Big-time beekeepers follow the crops, and then "rest" their bees, often in conservation areas in the Great Plains, trying to build up colony strength for the next round of crops.

Fruits are reproductive organs, formed to house and protect the developing seeds (and often to attract animals to eat the fruit and spread the seeds). Fruits form when boy meets girl -- when pollen meets egg. Wind transports pollen for many plants, but some cannot make the connection without help from an animal pollinator -- a bat, a hummingbird, or more commonly a pollinating insect like a bee.

What's at stake in the decline of pollinators? A lot of food, and a lot of wild plants, the experts say. According to Claire Kremen, an associate professor of environmental sciences at the University of California at Berkeley, 75 percent of our food crops involve some animal pollination.

Because corn, potatoes and rice do not require animal pollination, the majority of our calories are not at issue here. But a staggering list of crops, including melons, apples, nuts, and yes, cacao, the source of chocolate, require animals to move pollen, or produce better fruits, when animals are available for pollination.

Three raspberries. Left is small and misshapen, center is slightly bigger, right is large and healthy
Even crops that don't, strictly speaking, require pollination, do much better when an insect transfers pollen to the style, which transports pollen to the egg. Raspberries after passive self-pollination (left and middle) and insect pollination (right).

Did we mention coffee, watermelon and tomato?

In all, pollinators contribute $14 billion annually to the American food supply. Although we're concentrating on crops, bees, flies, moths, butterflies, hummingbirds and bats are also needed to pollinate an estimated 90 percent of wild flowering plants.

New, or more of the same

As beekeepers, government regulators and biologists try to decipher the cause of colony collapse disorder, there are more questions than answers. For example: Is CCD really something new? Some honeybee colonies always die out over the winter, and many stresses have long confronted bees:

little bee Nutrition. Bees need to eat pollen (for protein) and nectar (for sugar and some amino acids) pretty much all summer, and they benefit from a varied diet. Shortages of alternate food sources, especially around large farm fields, constrain their diet.

little bee Parasites. The worst bee parasite, the varroa mite, entered the United States around 1987. Varroa wreaks havoc on honeybee colonies by sucking out circulatory fluid and spreading viral disease, and the mite has some immunity to most mite-killing chemicals.

little bee Diseases. A wide range of bacteria and viruses afflict bees. The newly discovered Israeli Acute Paralysis Virus was linked to colony collapse. Initially fingered as a putative cause of CCD, the virus may in fact turn out to be just another insult.

little bee Trucker's blues. Commercial honeybees lead a migratory existence, riding 18-wheelers hundreds or thousands of miles to reach blooming crops, and then set free (often in conservation areas in the Great Plains) to rest and recover their energy. Transportation can spread disease and parasites: Australian bees shipped to California for the almond harvest are blamed for introducing the Israeli virus.

little bee Pesticides. Chemicals that farmers use to protect their crops can be deadly to bees, especially when used in combination. Ironically, many of these chemicals are used by beekeepers themselves to control mites. The newer neonicotinoid insecticides, used on farms and forests, preferentially attack the insect nervous system. That makes them safer for us, but they may be worse for bees, because they enter the plant and are transported into pollen and nectar. Some European countries have banned Imidacloprid, a widely popular neonicitinoid, due to concerns about harm to bees.

Close-up of bee collecting pollen from a white almond blossom rolls over to Close-up of a pile of raw, shelled almonds
Many lovable fruits and nuts, including the almond, are dependent on insect pollinators, especially bees. Check the rollover.

Given the many problems that honeybees have faced, it's hard to know if colony collapse is something distinct or just an extension of several problems. "I believe it results from some synergy due to all these stressors on bees," says Mace Vaughn, of the pollinator conservation program at the Xerces Society. "There are chronic problem with varroa mites, which have the ability to transmit disease, a slew of viruses, bacteria and fungi. If you add the stress of pesticides and poor nutrition, not enough pollen diversity in the diet, you get bees that are right at the edge. Something has pushed them over a balance point, so the colony can no longer maintain itself. It's hard for me to see this as the result of a new disease, but it may be, or of a systemic pesticide."

 Graph starts at 4.5 million in 1939, peaks at 6 million in 1947, ends at just over 2 million in 2008
Courtesy, Journal of Apicultural Research, 1
The number of bee colonies in the United States has steadily declined since 1940.

Pesticides and colony collapse

Certainly, beekeepers have been complaining about farm chemicals, especially insecticides, for many years. The case is hard to prove, if only because in CCD, by definition, the dead bees do not return to the hive for chemical analysis.

However a study published earlier this year 2 does suggest a role for pesticides in bee decline. After looking at 887 samples of bees and other items found in hives, Christopher Mullin and colleagues found a total of 121 pesticides and breakdown products.

 Small plane flying over large, green agricultural field and spraying a chemical on the field
New evidence implicates pesticides as a primary cause of bee colony collapse.

"Almost 60% of the 259 wax and 350 pollen samples contained at least one systemic pesticide," the researchers wrote. Ironically, some of the most common chemicals are those used by beekeepers to kill the varroa mite, which is resistant to chemical controls.

"It was surprising," Mullin, a professor of insect toxicology at Penn State, told the Why Files. "You can say we were alarmed to see the levels, numbers and diversity of pesticides present within the hive and its products. As a chemist, I'd expected to see one or two chemicals per sample. I was not expecting to see 39 pesticides in one sample, was not expecting the concentrations we saw."

Although honey was comparatively clean in the analyses, Mullin says the honeybee diet is polluted with so many chemicals that the overall impact is unpredictable. "It's like asking your doctor about the effects of taking 32 drugs together," even if each one is safe. "The doctor really can't answer that question, and you have become more of an experiment."

What role does Mullin think pesticides play in CCD? "If you'd asked me a year or two ago, I'd have said chemicals are one of multiple factors. With such a diversity of chemicals present, there are going to be side effects, and they are likely to make bees more susceptible to disease, to parasites like varroa, and to nutritional challenges."

Based on the accumulating evidence, Mullin says, "I have become more certain that pesticides are a primary cause" of CCD. "They are stressing the organism to the point where it is not able to cope with other stressors, with viruses and with the varroa mite."

If honeybees fail, can native pollinators take over?

Terry Devitt, editor; S.V. Medaris, designer/illustrator; Jenny Seifert, project assistant; David Tenenbaum, feature writer; Amy Toburen, content development executive

©2017, University of Wisconsin, Board of Regents.