Long-term study shows pesticides are killing bees

A major 18-year study of English bees is linking a controversial pesticide to precipitous declines in wild bee populations.

First Look

The worldwide decline of bees is something long-observed, a trend that garners both investigation and a search for solutions.

What exactly lies behind this unwelcome pattern is a matter that yields much debate, but one of the culprits that often comes in for criticism is the use of pesticides, specifically neonicotinoids. Now, in a study that considered a period stretching over 18 years, the evidence against those chemicals has grown.

The work, published Tuesday in Nature Communications, found that wild bee populations in England that foraged on neonicotinoid-treated oilseed rape were three times as negatively affected, compared with populations that foraged elsewhere.

"This is the first good evidence that bees are affected at the population level by the widespread use of neonicotinoids," Henrik Smith, a behavioral and conservation ecologist from Lund University in Sweden, who was not involved with the research, told the BBC.

The study was led by the Centre for Ecology and Hydrology, and it considered data regarding the population changes in 62 wild bee species, collected between 1994 and 2011 – a period that incorporates the widespread introduction of neonicotinoids in British agriculture.

The use of these pesticides was limited by the European Union two years ago after research had highlighted the risks they pose to bees, creatures critical to the pollination of numerous crops. But the chemicals had already been licensed for use in the UK since 2002, and by 2011, according to this latest study, the proportion of oilseed rape in British fields being treated with neonicotinoids had reached 83 percent.

To some, this study adds a crucial piece to the evidence stacking up against these pesticides, as Christopher Connolly, a neurobiologist and bee expert at the University of Dundee, who was not directly involved in this research, told Reuters: "The evidence against neonicotinoids now exists in key bee brain cells involved in learning and memory, in whole bees, entire colonies and now at the level of whole populations of wild bees."

Others say, however, that it does not prove causation, merely association.

“This study is another interesting piece to an unsolved puzzle about how neonicotinoid seed treatments affect bees,” bee health specialist Chris Hartfield of the National Farmers Union said in a statement. “It does not show that neonicotinoids are causing widespread declines in pollinator populations and it certainly does not show that neonicotinoid use has caused any extinction of bees in England.”

As Dr. Hartfield points out, the situation is far from simple. If farmers are to grow oilseed rape, then they need a way to defend against creatures other than bees that also enjoy feeding on the crops, some of whom cause great harm. In particular, the cabbage stem flea beetle is held responsible for wiping out huge swathes of the crop, and it is principally to combat this pest that neonicotinoids are used.

The study’s lead author, Ben Woodcock, is cognizant of this, saying there is an “underlying reality,” whereby if you are to grow oilseed rape, “you can’t do it without pesticides.”

"Just because you say 'don't use neonicotinoids anymore', the likelihood is that another pesticide is going to have to be used to compensate for that, [and] that is going to have impacts on runoffs into waterways and on other species," Woodcock told the BBC. "It needs to be taken in a very holistic perspective."