[Pollinator] Bee studies stir up pesticide debate

[Matthew Shepherd]

FROM: Nature

http://www.nature.com/news/bee-studies-stir-up-pesticide-debate-1.17366


Bee studies stir up pesticide debate

The threat that neonicotinoids pose to bees becomes clearer.



Daniel Cressey

22 April 2015



The case for restricting a controversial family of insecticides is growing.
Two studies published on 22 April in *Nature*1, 2 address outstanding
questions about the threat that the chemicals pose to bees, and come as
regulators around the world gear up for a fresh debate on pesticide
restrictions.



Many bee populations are in steep decline, with multiple causes identified,
including parasites and the loss of food sources. Also blamed are
neonicotinoids, a widely used class of insecticides that are often applied
to seeds, and find their way into the pollen and nectar of plants. The use
on seeds of three — clothianidin, imidacloprid and thiamethoxam — is
temporarily banned in the European Union because of concern that they might
harm pollinators; the ban is up for review in December. In the United
States, there are no such restrictions, but the US Environmental Protection
Agency said on 2 April that it was “unlikely” to approve new outdoor
neonicotinoid-pesticide uses without new bee data.



So far, the data are mixed. Many studies that link the poor health of bee
colonies to the pesticides have been criticized, for example for not using
realistic doses. Some defenders of the chemicals have argued that if
neonicotinoids are harmful, bees will learn to avoid treated plants.



Geraldine Wright, an insect neuroethologist at Newcastle University, UK,
and her colleagues investigated this aspect. They confined honeybees (*Apis
mellifera*) and bumblebees (*Bombus terrestris*) to boxes and gave them a
choice between plain nectar and nectar laced with imidacloprid,
thiamethoxam or clothianidin. The researchers found that the bees showed no
preference for the plain nectar. In fact, the insects were more likely to
choose the nectar containing imidacloprid or thiamethoxam1, although it is
not clear whether the preference would occur in the wild.



Wright’s team also analysed the response of the bees’ taste neurons to
neonicotinoids, and found that they reacted the same regardless of
concentration — indicating that the bees cannot taste the pesticides and
that the preference is caused by some other mechanism. Other studies have
shown that neonicotinoids activate receptors in bee brains linked to memory
and learning.



In contrast to Wright and colleagues’ work, the second paper2 looked at
honeybees and wild bees, including bumblebees, in the field. Maj Rundlöf,
an ecologist at Lund University in Sweden, and her colleagues analysed
eight fields of oilseed rape sown with seeds treated with clothianidin and
eight fields sown with untreated seeds across southern Sweden.



Honeybees did not respond differently in the treated and untreated fields.
But the researchers found that wild-bee density in treated fields was
around half that in untreated fields. Nests of solitary bees and
bumblebee-colony growth were also reduced in treated fields. “I’m worried
about the effects on wild bees,” says Rundlöf.



She suggests that honeybees have larger colony sizes, which could sustain
higher losses of foraging bees before showing overall health effects. But
that suggests another problem. “Honeybees are the model organism that is
used in toxicity testing for pesticides,” she says. If they are not
representative of bees in general, it could explain why more studies have
not detected negative effects.



Dave Goulson, a bee researcher at the University of Sussex in Brighton, UK,
also suspects that honeybees are more resilient than wild bees to
neonicotinoids. Rundlöf’s paper is “probably the best field study done so
far”, he says, and avoids many previous problems, such as contaminated
controls. “Any reasonable person would have to accept this is a real
effect,” he adds.



The debate is heating up. In March, Goulson reanalysed3 data from a 2013
study by the UK Food and Environment Research Agency (see
go.nature.com/w9jlti), which had concluded that neonicotinoid pesticides do
not harm bees: Goulson found that they do. In the same month, work from the
United States found4 that the probable harm from exposure to imidacloprid
in seed-treated crops was “negligible” in honeybees, and last year a study5
done in Canada reached a similar conclusion for clothianidin on oilseed
rape.



Christopher Connolly, who studies human and bee neuroscience at the
University of Dundee, UK, and has published work6 showing that
neonicotinoids interfere with neuron function in bumblebees, says that he
was already convinced that the pesticides are bad for bees. Now, “the
questions need to move to a different level”, to elucidate the mechanisms.



Nature

520,

416

(23 April 2015)

doi:10.1038/520416a


References

1.      Kessler, S. C. *et al*. Nature http://dx.doi.org/10.1038/nature14414
(2015).

2.      Rundlöf, M. *et al*. Nature http://dx.doi.org/10.1038/nature14420
(2015).

3.      Goulson, D. PeerJ 3, e854 (2015).

4.      Dively, G. P., Embrey, M. S., Kamel, A., Hawthorne, D. J. & Pettis,
J. S. PLoS ONE 10, e0118748 (2015).

5.      Cutler, G. C., Scott-Dupree, C. D., Sultan, M., McFarlane, A.
D. & Brewer,
L. PeerJ 2, e652 (2015).

6.      Moffat, C. *et al*. FASEB J. http://dx.doi.org/10.1096/fj.14-267179
(2015).
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