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CATCH THE BUZZ
Neonicotinoids let virus thrive in bees – Another nail in the
Neonic Coffin?
From Chemistry World
Scientists in Italy believe they have found a molecular trigger by
which neonicotinoid pesticides may
harm colonies of honey bees. The team’s experiments suggest that
exposure to neonicotinoids results in increased levels of a particular protein
in bees that inhibits a key molecule involved in the immune response, making
the insects more susceptible to attack by harmful viruses.
Francesco Pennacchio, of the University of Naples Federico II, and colleagues
identified a gene in insects that codes for a protein family similar to that
found in other animals that is known to regulate the immune response. This
leucine-rich repeat protein family, or LRR, has been shown to suppress the
activity of a key protein involved in immune signaling, called NF-κB. When the
researchers exposed bees to sub-lethal doses of the neonicotinoid clothianidin they saw a significant increase in the expression of the gene
encoding the LRR protein, and a concomitant suppression of the NF-κB signalling
pathway. These effects were not seen when bees were exposed to the
organophosphate insecticide chlorpyriphos.
When the team
infected bees with a common pathogen – deformed wing virus – and exposed them
to clothianidin and another neonicotinoid, imidacloprid,
at concentrations similar to those that would be found in the field, there was
significantly increased replication of the virus, which was not seen either in
untreated bees, or those exposed to chlorpyriphos. The virus is common in bees
and usually remains inactive – kept in check by the bees’ immune system. The
results suggest that insecticide-induced suppression of bees’ immune systems
lets the virus replicate unchecked.
‘The reported
effect on immunity exerted by neonicotinoids will allow additional
toxicological tests to be defined to assess if chronic exposure of bees to
sub-lethal doses of agrochemicals can adversely affect their immune system and
health conditions,’ says team member Francesco
Nazzi of the University of Udine. ‘Moreover, our data indicate the
possible occurrence in insects, as in vertebrates, of a neural modulation of
the immune response. This sets the stage for future studies in this research
area, and poses the question on how neurotoxic substances may affect the immune
response.’
Susan Kegley runs
the Pesticide Research Institute, an independent consultancy in the US. She
tells Chemistry World: ‘The EU has already implemented a minimum two-year
suspension of the use of the most toxic neonicotinoid insecticides –
clothianidin, imidacloprid and thiamethoxam
– on bee-attractive crops, to take effect December 1, 2013. The US EPA
[Environmental Protection Agency] remains unconvinced that neonicotinoids could
be a primary factor in recent pollinator population declines. This new study,
in conjunction with other observational studies showing enhanced susceptibility
to pathogens caused by exposure to neonicotinoids, should prompt US EPA to re-evaluate
the science.’