Nearly two decades of data reinforce concerns that pesticides are really bad for bees.

beesAdapted from article by Chelsea Harvey, Washington Post

New research has provided some of the strongest evidence yet that pesticides can do serious, long-term damage to bee populations. The new study examines the question of whether the use of a common (and highly controversial) class of pesticides called neonicotinoids can be linked to wild bee declines in England. The results suggest that this could be the case.

Using 18 years of data collected on more than 60 bee species in England, the researchers found that species foraging on pesticide-treated crops have experienced much more severe losses than species foraging on other plants. The study provides some of the first evidence that the effects of neonicotinoid exposure can cause major damage to bees. “It’s nice to see the use of long-term data to look at trends in pesticide impacts over longer time scales,” said Dara Stanley, a plant ecology lecturer at the National University of Ireland Galway, by email. (Stanley has previously conducted research on the effects of neonicotinoids in bees, but was not involved with the new study.) “That is something that has been missing in the debate on bees and pesticides so far, and there have been many calls to look at effects over time.”

In 2013, the European Union placed a ban on the use of multiple neonicotinoid pesticides, citing their potential danger to bees, although a few exemptions have since been allowed in the United Kingdom. Neonicotinoids are still widely used in many other places around the world, including in the United States. They’re produced by a number of different manufacturers and include household names such as Bayer’s Admire Pro insecticide, which includes a neonicotinoid called imidacloprid, or Syngenta’s Actara insecticide, which contains thiamethoxam. Until now, most of the research on their effects has been limited to short-term, small-scale studies, many of them performed in laboratory settings, said Ben Woodcock, an ecological entomologist at the Centre for Ecology and Hydrology in the U.K. and the paper’s lead author. They’ve also tended to focus on just a few species. The new study, on the other hand, relies on field data collected on many species over nearly two decades.

The researchers focused on the different responses between bee species that forage on pesticide-treated oilseed rape crops — the same plants commonly used to make canola oil — and bees that forage on other plants. Oilseed rape crops are widely treated with neonicotinoids around the world, and the practice began on a wide scale in the U.K. starting in 2002.  It’s the biggest mass flowering crop in the U.K. where neonicotinoids have been widely applied, according to Woodcock, making it an ideal subject for the study.

The researchers were interested in finding out whether bee species that forage on oilseed rape plants have experienced greater declines than bee species that don’t. So they gathered nearly 20 years’ worth of data, mostly collected in surveys by citizen scientists between 1994 and 2011, on where bee species have been spotted and what plants they foraged on. Different species often prefer to snack on different plants, and some of the included species visited oilseed rape plants while others didn’t do so at all. The researchers incorporated all the data, along with information on oilseed rape cover and pesticide use in the U.K., into a model that helped them analyze all the information.

The findings support the previous research which indicates that neonicotinoids can have damaging effects on bees — and they also suggest that these effects could result in serious population declines on a large scale in the long term.

In the meantime, scientists from Bayer Crop Science, a major manufacturer of neonicotinoid pesticides, took issue with the study’s correlational findings, which they’ve pointed out cannot be used to argue with certainty that pesticides cause declines in bees. A statement from the company, sent to The Washington Post by Bayer spokesperson Jeffrey Donald, summarized their complaint.

“The authors chose to investigate only one potential factor, namely neonicotinoid insecticides,” the statement said. “This was chosen out of many different factors which may have an influence on the development of wild bees, for example landscape structures, climatic conditions, availability of specific foraging plants and nesting habitats. It is a well-known fact that the structure of agricultural landscapes in large parts of Europe has changed substantially in the last decades. The area of landscape structures available for nesting or foraging, especially for specialized species, has significantly declined, resulting in fewer habitats for pollinators.”

“Bees have been undergoing declines for a long time and it’s been linked to a number of things — habitat fragmentation, climate change,” Woodcock said. “This is a contributing factor to bee declines, it’s not the sole cause. If you stop using neonicotinoids tomorrow, you wouldn’t solve the problem.” But many experts feel that limiting their use would certainly help. Krupke, the Purdue entomologist said “But I think in areas where pesticides are used extensively…that pesticides are high on the list of concern.”

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