Exposure to a widely used pesticide affects the development of worker bumblebees, leading to the bees hatching out at a smaller size than they otherwise would, according to a new study by bee experts at Royal Holloway University in London.

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Researchers at Royal Holloway were behind one of the studies on pesticides and bee health published in the journal Science in 2012 which attracted the attention of the European Food Safety Authority and led the Commission to introduce a partial ban on neonicotinoids last year.

Fresh research, published today in the Journal of Applied Ecology, shows that prolonged exposure to a pyrethroid pesticide, which is used on flowering crops to prevent insect damage, reduces the size of individual bees produced by a colony. Researchers Gemma Baron, Dr Nigel Raine and Professor Mark Brown from the School of Biological Sciences at Royal Holloway worked with colonies of bumblebees in their laboratory and exposed half of them to the pesticide.

The scientists tracked how the bee colonies grew over a four month period, recording their size and weighing bees on micro-scales, as well as monitoring the number of queens and male bees produced by the colony.

Commenting on the findings, Gemma Baron said, "We already know that larger bumblebees are more effective at foraging. Our result, revealing that this pesticide causes bees to hatch out at a smaller size, is of concern as the size of workers produced in the field is likely to be a key component of colony success, with smaller bees being less efficient at collecting nectar and pollen from flowers."

The Royal Holloway team said their study is the first to examine the impact of pyrethroid pesticides across the entire lifecycle of bumblebees. The topical research was conducted to inform a national Bee Health Conference running in London from Wednesday to Friday this week (22-24 January 2014).

Given the current EU moratorium on the use of three neonicotinoid pesticides, the use of other classes of pesticide, including pyrethroids, is likely to increase, according to the Royal Holloway scientists.

Dr Nigel Raine, who will be speaking at the coming bee conference, said, "Our work provides a significant step forward in understanding the detrimental impact of pesticides other than neonicotinoids on wild bees. Further studies using colonies placed in the field are essential to understand the full impacts, and conducting such studies needs to be a priority for scientists and governments."

Moratorium on neonicotinoids

Last year, reacting to the Commission's introduction of tight restrictions on three neonicotinoid pesticides Dr Raine said, "Whether this moratorium will benefit bees depends on what alternative methods of pest control are used instead.  If the ban results in greater use of crop sprays the net result could be worse.  More research is needed to determine if this will be the case.  

"Bees are actually exposed to multiple pesticides when they forage in the field.  The risk assessment for pesticides needs to take into account this type of combinatorial exposure as well as potential sublethal behavioural effects and longer term (chronic) impacts… We need to ensure that pesticides are used in ways that minimise any detrimental impact on insect pollinators."

Also commenting on the EU restrictions, and reacting to industry claims that the restrictions would have serious implications for growers of some of Europe's most important field crops, David Goulson, Professor of Biological Sciences at the University of Sussex, said, "There is no evidence that the withdrawal of these compounds will have significant negative impacts on farming.  It is high time we returned to Integrated Pest Management (IPM) – an approach focussed on minimising pesticide use, maximising the number of biological control agents, using cultural controls such as crop rotations, and monitoring pest numbers so that chemical controls only need be applied when there is a problem.

"Instead, neonicotinoids are applied prophylactically, much like taking antibiotics to avoid getting ill – and this use on crops such as wheat will continue after the partial ban.  This is a recipe for environmental damage and the evolution of resistance in pests."