AgroPages-Study finds correlation between imidacloprid and bee colony losses-Agricultural news

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A major study has identified a correlation between the use of the neonicotinoid imidacloprid and honey bee colony losses across England and Wales.

The study, led by Giles Budge from Defra’s Food and Environment Research Agency (Fera) made a number of other notable findings, including proof that farmers who use neonicotinoid seed treatments use fewer foliar sprays.

It also found little benefit to farmers overall in terms of increased yields from use of the chemicals, although there was significant variation over time.

The study, published in the scientific journal Nature, combined large datasets large-scale pesticide usage, oilseed rape yield, weather and honey bee colony losses over 11 years to investigate the potential costs to pollinators and benefits to farmers of neonicotinoid seed coatings on OSR at a national level.

The data showed the total cropped area of OSR for England and Wales doubled between 2000 and 2010 to more than 600,000 ha, with use of neonicotinoid seed treatments increasing dramatically – from 1 per cent of the planted area in 2000 to 75 per cent in 2010.

Against this there were 126,220 bee colony observations, of which 10,725 colonies (8.5 per cent) were found to be dead.

Once regional differences had been accounted for, the researchers found usage of Bayer’s imidacloprid on OSR ‘had a positive relationship with honey bee colony losses such that increased regional usage was linked to higher honey bee colony losses’.

The observational data predicted differences in colony mortality of 10 per cent between low and high field exposure of imidacloprid.

Foliar sprays

While the study will undoubtedly add fuel to the fire of those campaigning for a permanent ban on neonicotinoids, it also highlighted some of the benefits of the seed treatments.

Observations from over 76,000 ha of OSR over five years provided what the researchers said was ‘the first evidence that farmers who used imidacloprid seed coatings consistently reduced the number of foliar insecticide sprays used in the autumn, but not during flowering’.

The study also tried to gauge whether farmers using neonicotinoid seed treatments increased their yield or profit when compared to OSR crops grown with no seed treatment but with foliar insecticides.

The results were mixed, demonstrating, for example, that while farmers did experience significant yield increases in 2004 and 2006 for imidacloprid and in 2010 for thiamethoxam, there was no consistent effect of imidacloprid seed coating on yield over all years.

The effects of imidacloprid seed treatment on the yield of oilseed rape were negative in 2008, suggesting, according to the researchers, reduced pest control compared to crops that received no insecticide seed treatment following a wet summer.

Overall, the researchers said the study showed the economic justification for using neonicotinoids to treat OSR seed was ‘dynamic and sometimes financially beneficial to farmers’.

But they stressed their research did not provide definitive answers on the trade-off between the benefits of pesticides against their collateral environmental damage.

Adverse weather

Dr Budge, head of crop science also stressed honey bee colony losses were also linked to adverse weather, as well as usage of imidacloprid, and showed regional patterns, with beekeepers in Wales suffering consistently high losses.