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2nd study links pesticide to bee epidemic

April 5, 2012
Courtesy of the Harvard School of Public Health
and World Science staff

The likely cul­prit in sharp world­wide de­clines in hon­ey­bee col­o­nies since 2006 is im­i­da­clo­prid, one of the most widely used pes­ti­cides, a study from the Har­vard School of Pub­lic Health in­di­cates.

It’s the sec­ond re­port to link that pes­ti­cide or closely re­lat­ed ones to the mys­ter­ious bee die-offs, though the pre­vi­ous one fo­cused on die-offs in Eu­rope pri­marily and used a dif­fer­ent meth­od­ol­o­gy.

Mem­bers of the Har­vard group, led by bi­ol­o­gist Al­ex Lu, a spe­cial­ist in en­vi­ron­men­tal ex­po­sure, said they found “con­vinc­ing ev­i­dence” of the link be­tween im­i­da­clo­prid and a phe­nom­e­non called Col­o­ny Col­lapse Dis­or­der, in which adult bees aban­don their hives in droves.

The study is to ap­pear in the June is­sue of the Bul­le­tin of In­sec­tol­o­gy.

“The sig­nif­i­cance of bees to ag­ri­cul­ture can­not be un­der­es­ti­mat­ed,” said Lu. “And it ap­par­ently does­n’t take much of the pes­ti­cide to af­fect the bees. Our ex­pe­ri­ment in­clud­ed pes­ti­cide amounts be­low what is nor­mally pre­s­ent in the en­vi­ronment.”

Bees, be­yond pro­duc­ing hon­ey, are prime pol­li­na­tors of roughly one-third of the crop spe­cies in the U.S., in­clud­ing fruits, veg­eta­bles, nuts, and live­stock feed such as al­fal­fa and clo­ver. Mas­sive loss of hon­ey­bees could re­sult in bil­lions of dol­lars in ag­ri­cul­tur­al losses, ex­perts es­ti­mate.

Lu and his co-authors hy­poth­e­sized that the uptick in col­o­ny col­lapse dis­or­der re­sulted from im­i­da­clo­prid, a mem­ber of a family of pes­ti­cides known as neon­i­coti­noids in­tro­duced in the early 1990s. Bees can be ex­posed in two ways: through nec­tar from plants or through high-fructose corn syr­up bee­keep­ers use to feed their bees. (Since most U.S.-grown corn has been treated with im­i­da­clo­prid, it’s al­so found in corn syr­up.)

In the sum­mer of 2010, the re­search­ers con­ducted a field study in Worces­ter Coun­ty, Mass. Over a 23-week pe­ri­od, they mon­i­tored bees in four dif­fer­ent bee yards; each yard had four hives treated with dif­fer­ent lev­els of im­i­da­clo­prid and one non-treated hive. Af­ter 12 weeks, all the bees were alive. But af­ter 23 weeks, 15 out of 16 of the treated hives had died. Those ex­posed to the high­est lev­els of the pes­ti­cide died first.

The pre­vi­ous, Eu­ropean study fo­cused on neon­i­coti­noids more gen­er­al­ly, and em­ployed a dif­fer­ent meth­od­ol­o­gy.

Lu said the char­ac­ter­is­tics of the dead hives in his study were con­sist­ent with col­o­ny col­lapse dis­or­der; the hives were emp­ty ex­cept for food stores, some pol­len, and young bees, with few dead bees near­by. When oth­er con­di­tions cause hive col­lapse—such as dis­ease or pest­s—many dead bees are typ­ic­ally found in­side and out­side the af­fected hives.

Sci­en­tists, pol­i­cy­makers, farm­ers, and bee­keep­ers, alarmed at the sud­den losses of be­tween 30 per­cent and 90 per­cent of hon­ey­bee col­o­nies since 2006, have posed many the­o­ries as to the cause of the col­lapse, such as pests, dis­ease, pes­ti­cides, mi­gra­to­ry bee­keep­ing, or some com­bina­t­ion of these fac­tors.


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The likely culprit in sharp worldwide declines in honeybee colonies since 2006 is imidacloprid, one of the most widely used pesticides, a study from Harvard School of Public Health indicates. It is the second report to link that pesticide or closely related ones to bee die-offs, though the previous one focused on bee die-offs in Europe primarily and used a different methodology. Members of the Harvard group, led by biologist Alex Lu, a specialist in environmental exposure, said they found “convincing evidence” of the link between imidacloprid and a phenomenon called Colony Collapse Disorder, in which adult bees abandon their hives in droves. The study is to appear in the June issue of the Bulletin of Insectology. “The significance of bees to agriculture cannot be underestimated,” said Lu. “And it apparently doesn’t take much of the pesticide to affect the bees. Our experiment included pesticide amounts below what is normally present in the environment.” Bees, beyond producing honey, are prime pollinators of roughly one-third of the crop species in the U.S., including fruits, vegetables, nuts, and livestock feed such as alfalfa and clover. Massive loss of honeybees could result in billions of dollars in agricultural losses, experts estimate. Lu and his co-authors hypothesized that the uptick in colony collapse disorder resulted from imidacloprid, a member of a family of pesticides known as neonicotinoids introduced in the early 1990s. Bees can be exposed in two ways: through nectar from plants or through high-fructose corn syrup beekeepers use to feed their bees. (Since most U.S.-grown corn has been treated with imidacloprid, it’s also found in corn syrup.) In the summer of 2010, the researchers conducted a field study in Worcester County, Mass. aimed at replicating how imidacloprid may have caused the outbreak. Over a 23-week period, they monitored bees in four different bee yards; each yard had four hives treated with different levels of imidacloprid and one non-treated hive. After 12 weeks, all the bees were alive. But after 23 weeks, 15 out of 16 of the imidacloprid-treated hives—94%—had died. Those exposed to the highest levels of the pesticide died first. The previous, European study focused on neonicotinoids more generally, and employed a different methodology. Lu said the characteristics of the dead hives in his study were consistent with colony collapse disorder; the hives were empty except for food stores, some pollen, and young bees, with few dead bees nearby. When other conditions cause hive collapse—such as disease or pests—many dead bees are typically found inside and outside the affected hives. Scientists, policymakers, farmers, and beekeepers, alarmed at the sudden losses of between 30% and 90% of honeybee colonies since 2006, have posed many theories as to the cause of the collapse, such as pests, disease, pesticides, migratory beekeeping, or some combination of these factors.