(Beyond Pesticides, September 6, 2011) Scientists in France have discovered that honey bees are at a higher risk of dying from infection by Nosema ceranae (N. ceranae) when they are exposed to low doses of insecticides. The results, presented in the journal PLoS ONE, support the theory that combining more N. ceranae with high pesticide content in beehives could contribute to colony depopulation.
The French study, “Exposure to Sublethal Doses of Fipronil and Thiacloprid Highly Increases Mortality of Honeybees Previously Infected by Nosema ceranae,” brought together researchers from the Laboratoire Microorganismes: Génome et Environnment and the Laboratoire de Toxicologie Environnment who utilized their respective skills in parasitology and toxicology to assess the effect of pathogen/toxin interactions on bee health. In the laboratory, the researchers chronically exposed newly emerged honey bees, some healthy and others infected with Nosema ceranae, to low doses of insecticides: fipronil and thiacloprid. They found that the infected bees died when they were chronically exposed to insecticides, even at sublethal doses, unlike the healthy bees. This combined effect on honeybee mortality was observed with daily exposure to extremely low doses (over 100 times less than the LD50 or dose needed to kill 50% of the sample population, for each insecticide).
This study shows that interaction between Nosema disease and insecticides represents a significant additional risk for bee populations, and could possibly explain certain cases of excess mortality. This work also finds that insecticide doses considered to be non-lethal have a lethal toxic potential for organisms that are infested with parasites and therefore vulnerable.
Honey bees across the U.S. have been disappearing in what scientists dub Colony Collapse Disorder or CCD. CCD has devastated bees and beekeepers around the country in recent years, a phenomenon that that many scientists have tied to the use of the systemic neonicotinoid insecticides widely used in agriculture and gardens. According to the survey, 30% of managed honey bee colonies across the country were lost over the winter. Over the past five years, since the discovery of CCD, annual winter colony losses have hovered near the 30% mark. A report released jointly by the U.S. Department of Agriculture’s (USDA) Agricultural Research Service (ARS) and the Apiary Inspectors of America (AIA) shows that losses of honey bee populations over the 2010/2011 winter remained abnormally high. The United Nations (UN) also revealed in a report that the collapse of honey bee colonies is now a global phenomenon.
Some European and U.S. scientists postulate that losses of biodiversity and food resources, due to climate change, have intensified the problem. Others believe that a rise in single-crop farming and modification of landscapes, as well as pathogens causing diseases like foulbrood and varroasis are responsible for the problem. While CCD appears to have multiple interacting, a range of evidence points to sub-lethal pesticide exposures and pathogens as important contributing factors. Neonicotinoids , the particularly suspect class of insecticides, especially in combination with the dozens of other pesticides, are found in honey bee hives. The use of chemicals in agriculture has been found to damage bees by weakening their immune systems. Laboratory studies show that some insecticides and fungicides can act together to be 1,000 times more toxic to bees. They can also affect the sense of direction, memory and brain metabolism, and herbicides and pesticides may reduce the availability of plants bees need for food and for the larval stages of some pollinators.
In December 2010, after the discovery of a leaked memo from the U.S. Environmental Protection Agency (EPA) citing flawed and missing scientific data regarding the registration of the neonicotinoid pesticide clothianidin, Beyond Pesticides, along with beekeepers and other environmentalists, called on EPA to remove clothianidin from the market. EPA responded by defending clothianidin and the agency’s pesticide review process, saying that they “are not aware of any data that reasonably demonstrates that bee colonies are subject to elevated losses due to chronic exposure to this pesticide.” However, the emerging science finds that pesticides like clothianidin and others mentioned above do in fact harm bees. See Beyond Pesticides’ factsheet on the connection between clothianidin and CCD. For more information, on honeybees and pesticides visit Beyond Pesticides’ Pollinators and Pesticides page.
Source: Environmental Protection Online