3 Studies Link Common Pesticides to Bee Decline (Slideshow)
Care2 Earth Month: Back to Basics
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Where have all the bees gone?
What is causing colony collapse disorder, when hives suddenly lose most of their worker bee population, with very few dead bees found nearby and only the queen and brood remaining?
Bees are worth about 1.8 billion pounds (about $2.9 billion) a year in the U.K., according to new research about the cost of hand-pollinating the many crops that bees do so for free. As Damian Carrington writes in the Guardian, hand-pollination is already a necessity in places like China’s pear orchards while in the U.S. bees are “routinely trucked around… to compensate for the loss of their wild cousins.” In the U.K., Carrington describes a virtual “bee-calypse”: “Half the UK’s honey bees kept in managed hives have gone, wild honey bees are close to extinction and solitary bees are declining in more than half the place they have been studied.”
Carrington cites the loss of meadows full of flowers and parasites and diseases. But pesticides are routinely cited as a factor and three recent scientific studies offer compelling evidence linking pesticides to global declines in bee populations.
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Photo by expom2uk
(1) Pesticides Fog Honeybees’ Brains
In a study in the March issue of the journal Science, researchers at the National Institute for Agricultural Research in France fed bees sugar water laced with neonicotinoids. These insecticides are used as seed dressings, so they permeate all parts of the crops including pollen and nectar. The bees had miniature radio tags and were moved more than a half a mile from their hive.
In familiar territory, bees exposed to pesticides were 10 percent less likely to return home and only 31 percent less likely to do so in unfamiliar places. The chemicals cause “homing failure” in bees, so they are unable to find their way back to their hives. Using a computer model, the French scientists estimated that the hive’s population would then drop by two-thirds or more, depending on the number of worker bees exposed.
Some including a scientist for Bayer CropScience, the leading maker of neonicotinoids, and James Cresswell, an ecotoxicologist at the University of Exeter in England, have been critical of the study because it used a computer model. But May Berenbaum, an entomologist at the University of Illinois at Urbana-Champaign, said in the New York Times that she felt the study was “very well-designed.”
(2) Neonicotinoids Reduce the Growth of Bumblebee Colonies and the Production of Queens
In another study in Science, British researchers fed sugar water laced with a neonicotinoid to 50 bumblebee colonies. They moved the bee colonies to a farm beside 25 colonies that had been fed ordinary sugar water.
Colonies exposed to the pesticides produced 85 percent fewer queens. Such a decline would translate into 85 fewer colonies.
All the bees in a colony die at the of a year except for a few new queens, which go on to produce new hives. But if far fewer queens are produced, there will be far fewer bees colonies, period.
(3) Widely-used Pesticide Imidacloprid Linked to Colony Collapse Disorder
In an study published in the April issue of the Bulletin of Insectology, Alex Lu, associate professor of environmental exposure biology in the Department of Environmental Health at Harvard University, focused on one neonicotinoid that was introduced in the 1990s, imidacloprid. Bees can be exposed to this chemical either through nectar from plants or from high-fructose corn syrup that beekeepers use to feed their bees. Most corn in the U.S. is treated with imidacloprid, so it is found in corn syrup.
For 23 weeks, the scientists monitored bees in four different bee yards, each of which had been treated with different levels of imidacloprid, and one control hive. All the bees were alive after 12 weeks of imidacloprid dosing. After 23 weeks, 15 of the 16 imidacloprid-treated hives had perished and those exposed to the highest levels of the pesticide were the first to die.
The dead hives showed the characteristics of colony collapse: empty hives with food stores, some pollen and young bees, and only a few dead bees nearby. Had a virus or pest caused hive collapse, there would have been many dead bees inside the hive.
Lu says that his study offers “convincing evidence” connecting imidacloprid to colony collapse disorder. He suggests removing all neonicotinoids from use across the globe for a period of five to six years; if the bee population increases afterwards, neonicotinoids can be clearly pointed to as a culprit.
As Carrington writes, there is no need for testing to see if pesticides harm bees. Even “sub-lethal doses” cause them “serious harm,” and the significance of bees to agriculture and to the global ecosytem is inestimable. What we need is a global ban on imidacloprid, before it is too late.