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Pesticides not yet proven guilty in bee dieoffs: study

Sept. 22, 2012
Courtesy of the University of Exeter
and World Science staff

Con­tra­ry to some pre­vi­ous stud­ies, crop pes­ti­cides are un­likely to cause dev­as­tat­ing de­clines in hon­ey­bee popula­t­ions, the au­thors of new re­search say.

Writ­ing in the Sept. 20 is­sue of the jour­nal Sci­ence, U.K. sci­en­tists from the Uni­vers­ity of Ex­e­ter and Food and En­vi­ron­ment Agen­cy said more work is needed to pre­dict the im­pact of widely-used ag­ri­cul­tur­al in­sec­ti­cides, called neon­i­coti­noids, on hon­ey­bees. The U.K. researchers in par­tic­u­lar took issue with one previous study that they said failed to cor­rectly re­flect the rate at which hon­ey­bee col­o­nies re­cov­er from los­ing mem­bers.

Sud­den losses of hon­ey­bee col­o­nies in the United States and Europe, esti­mated at be­tween 30 per­cent and 90 per­cent of col­o­nies since 2006 in the U.S. alone, have alarmed sci­en­tists, pol­i­cy­makers, farm­ers, and bee­keep­ers. Be­yond pro­duc­ing hon­ey, the in­sects are prime crop pol­li­na­tors.

Neon­i­coti­noids are among the most widely-used ag­ri­cul­tur­al in­sec­ti­cides. Hon­ey­bees in­gest residues of the chem­i­cals as they gath­er nec­tar and pol­len from treated plants. 

Pre­vi­ous re­search has been cit­ed by sci­en­tists, en­vi­ron­men­tal­ists and policy-makers as ev­i­dence of the fu­ture im­pact of these pes­ti­cides on hon­ey­bees, the au­thors of the Sci­ence study said.

Past re­search led by French sci­ent­ist Mikaël Hen­ry showed that the death rate of bees in­creased when they drank nec­tar laced with a neon­i­coti­noid pes­ti­cide, thi­amethoxam. It cal­cu­lat­ed that this would cause their col­o­ny popula­t­ion to col­lapse. The U.K. group said this re­search was probably in­stru­men­tal in the French gov­ern­men­t’s re­cent de­ci­sion to ban the use of thi­amethoxam, a neon­i­coti­noid used in Cruis­er OSR, a pes­ti­cide pro­duced by the Swiss com­pa­ny Syn­genta.

The new work ex­plains how the cal­cula­t­ion may have used an in­ap­pro­pri­ately low birth rate, said study au­thor James Cress­well of the Uni­vers­ity of Ex­e­ter. “We know that neon­i­coti­noids af­fect hon­ey­bees, but there is no ev­i­dence that they could cause col­o­ny col­lapse,” he added. The dras­tic hon­ey­bee popula­t­ion de­clines have been dubbed col­o­ny col­lapse dis­or­der.

“When we re­peat­ed the pre­vi­ous cal­cula­t­ion with a real­is­tic birth rate, the risk of col­o­ny col­lapse un­der pes­ti­cide ex­po­sure dis­ap­peared,” he added. “I am def­i­nitely not say­ing that pes­ti­cides are harm­less to hon­ey­bees, but… our re­search shows that the ef­fects of thi­amethoxam are not as se­vere as first thought.”


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Contrary to some previous studies, crop pesticides are unlikely to cause devastating declines in honeybee populations, the authors of new research say. Writing in the Sept. 20 issue of the journal Science, U.K. scientists from the University of Exeter and Food and Environment Agency said more work is needed to predict the impact of widely-used agricultural insecticides, called neonicotinoids, on honeybees. In particular, they argue that previous studies failed to correctly reflect the rate at which honeybee colonies recover from losing individuals. Neonicotinoids are among the most widely-used agricultural insecticides. Honeybees ingest residues of the chemicals as they gather nectar and pollen from treated plants. Previous research has been cited by scientists, environmentalists and policy-makers as evidence of the future impact of these pesticides on honeybees, the authors of the Science study said. They added that the research was probably instrumental in the French government’s recent decision to ban the use of thiamethoxam, a neonicotinoid used in Cruiser OSR, a pesticide produced by the Swiss company Syngenta. Past research led by French scientist Mikaël Henry, showed that the death rate of bees increased when they drank nectar laced with a neonicotinoid pesticide, thiamethoxam. It calculated that this would cause their colony population to collapse. The new work explains how the calculation may have used an inappropriately low birth rate, said study author James Cresswell of the University of Exeter. “We know that neonicotinoids affect honeybees, but there is no evidence that they could cause colony collapse,” he added. The drastic honeybee population declines have been dubbed colony collapse disorder. “When we repeated the previous calculation with a realistic birth rate, the risk of colony collapse under pesticide exposure disappeared,” he added. “I am definitely not saying that pesticides are harmless to honeybees, but… our research shows that the effects of thiamethoxam are not as severe as first thought.”