Scientists from the UK have found that pesticide exposure can affect colony development, days after research from American institutions and the US Department of Agriculture suggested that exposure to a concoction of chemicals in the field is harming colonies. Like their American counterparts, who followed honeybees kept for commercial pollination and honey production on their seasonal journey up the country’s Eastern Seaboard, researchers from Imperial College London looked at bees in the field to get results in the most true-to-life conditions possible.

Unlike the USDA research, the Imperial College (ICL) team was looking specifically at neonicotinoids, a new and widely used class of systemic insecticide (one that is taken up by the plant itself), which has come under scrutiny for effects on non-target insects and ecosystems. Three neonicotinoids have been subject to heavy restrictions in the EU since 2013, due to increasing evidence of their impacts on the health of bees, which are in decline across much of the world.

However, the ICL researchers said the extent to which neonicotinoids are to blame for declines is not clear; in fact, the USDA researchers who looked at bee colonies as ‘super-organisms’ and not at individual bees found certain commonly used fungicides, previously thought safe for bees, to be more strongly associated with colony failure. With strong feeling on either side of the debate, research in this area has been subject to intense scrutiny by environmental groups, farm interests and agchem manufacturers; lab studies are often criticised for being unrealistic, and field studies are difficult to control, meaning other factors in the environment could play a role in any observed impacts.

The ICL team tried design a balanced study, keeping bee colonies in the field, but closely monitoring their exposure to pesticide and any other activity and developments in the colonies. Bees were kept in a rural setting, but not near any farms to minimise their exposure to chemicals not being studied as part of the experiment. They were given a nectar substitute laced with a neonicotinoid, but were allowed to leave the colonies to forage. Researchers studied pollen the bees brought back whenever a bee returned to the hive.

Unlike some previous studies, they didn’t find any large effect on bee foraging behaviour following neonicotinoid exposure. However, they did find evidence that the colony produced a lower number of new queens and males, which underpin colony success. Senior author Dr Richard Gill from the Department of Life Sciences at Imperial commented, "Neonicotinoids found in the environment are unlikely to directly kill individual foraging bees, but when exposure is relatively persistent and combined with other stressors associated with land use change, they could have detrimental effects at the colony level."

Lead author Dr Andres Arce, also from the Department of Life Sciences at Imperial, added, "Sub-lethal effects like this are important to consider in pesticide risk assessments, and our study provides a helpful method to determine long-term effects on colony health in the field under controlled exposure."

Commenting on the impacts of the findings, Dr Christopher Connolly from the University of Dundee, who was not involved in the research, said, “This study investigates one of the three currently banned neonicotinoids and replicates previously published work and comes to the same conclusion, that clothiandin does not exhibit the same level of toxicity to bumblebees as demonstrated for imidacloprid or thiamethoxam.”

Dr Connolly continued, “This is important as it demonstrates further that neonicotinoids need to be considered independently. Moreover, other beneficial species are likely to have different sensitivities to each neonicotinoid.”