“Real-World” Tests Confirm Neonicotinoids Harm Bees

Amro Zayed explains how neonic pesticides can move from agricultural fields to natural habitats, harming honeybee workers and queens. | York University

Two of the first field test studies featuring real-world conditions have confirmed that the survival rates and reproduction abilities of bees are negatively affected by prolonged exposure to pesticides known as neonicotinoids. The studies were conducted in Europe and Canada.

"There's been a big debate about neonicotinoids," said Amro Zayed, co-author on the Canada-based study, and an associate professor in the department of biology at York University in Toronto. "Often, people criticize related research saying scientists use higher doses of these pesticides than are realistic, or apply them for a much longer time than would be seen in the field. The problem has been that we haven't really had good field data, so these criticisms have gone unanswered."

To address such concerns, Zayed and colleagues, as well as authors on the European study, conducted season-long monitoring of the use of neonicotinoids near bee colonies in agricultural settings in Ontario and Québec, Canada, and in 33 locations in Hungary, Germany and the U.K., respectively.

"Our study," said Richard Pywell, a science area lead in sustainable land management at the U.K. Centre of Ecology & Hydrology and co-author of the European research effort, "was designed… to reflect the real world in size and scope. We believe it goes a considerable way to explaining the inconsistencies in the results of past research."

The results of both teams, published in the 30 June issue of Science, reveal that while factors like the health of local bee colonies and the availability of food sources influence the impact of neonicotinoids, the pesticide's effects are largely negative.

In the 1990s, research into bee population health began suggesting neonicotinoids — applied broadly to major crops like corn and soybeans — were harming these key pollinators.

However, determining just how, and by how much, has yielded mixed results — not only because of questions around the realism of related studies, but also because parsing the contributing impacts of other threats to bees, such as climate change, has been difficult.

What's more, said Jeremy Kerr, professor in the department of biology at the University of Ottawa and author of a related Perspective in this issue, "some studies that have been carefully designed and executed have nevertheless found that neonics did not cause harm to [bees]."

In the first of two studies designed to provide a clearer picture of neonicotinoid-specific effects, Pywell's team performed "perhaps the most ambitious field experiment of neonicotinoid effects yet conducted," according to Kerr.

Working near oilseed rape crops seed-treated with neonicotinoids in Germany, Hungary, and the U.K., Pywell and colleagues gathered data on impacts to three bee species, finding neonicotinoids contributed to local declines in the population levels of the bees in each case — in unique ways depending on environmental context.

For example, in Hungary and the U.K., but not in Germany, exposure to neonicotinoid-treated crops reduced bees' ability to survive in the winter — a key measure of year-to-year viability. In all three countries, however, increasing neonicotinoid residue in the bee nests meant lower reproductive success, as reflected in lesser egg production.

The differing impacts on honeybees between countries, said the authors, may be associated with several interacting factors. "The colonies in the U.K. and Hungary were more weakened by disease than were those in Germany," said Pywell, "making them more susceptible to extra stress through neonicotinoid exposure."

Tsvetkov and her colleagues found that worker bees exposed to neonicotinoids exhibited lower life expectancies, by up to 23 percent. Also, their colonies were more likely to permanently lose queens. "And," added Zayed, "their flights got progressively longer and longer as they aged, as if they were having a hard time finding food, or their way home."

Neonicotinoids are used to "dress" seeds in order to target insects that would damage the adult plants that sprout from them. Notably, neonicotinoid seed coatings were banned in the European Union in 2013.

"The neonicotinoid moratorium gave us the opportunity to do this experiment," Pywell explained. "As neonicotinoids were not used elsewhere in the landscapes we studied, our controls (no neonicotinoids) were true controls. We obtained licenses from the appropriate authorities in each country to apply the neonicotinoids over specified areas."

In a second study, Zayed and his team, working in commercial corn-growing areas of Canada, sought to isolate neonicotinoid-specific impacts from other high-intensity agriculture threats.

The research team studied honey bee colonies in five locations close to corn grown from neonicotinoid-treated seeds. These colonies were extensively sampled and tested for pesticides from early May to September 2014.

The researchers reported that bees in these locations are being exposed to neonicotinoids for three to four months. "That is most of the active bee season in temperate North America," said York University Ph.D. student, and study first author, Nadia Tsvetkov.

Tsvetkov, Zayed and colleagues were also surprised to observe that the neonicotinoid-contaminated pollen collected by the bees came not from crops grown from neonicotinoid-treated seeds, but from plants like clover growing nearby. "This indicates that neonicotinoids spill over from agricultural fields into the surrounding environment, where they are taken up by other plants that are very attractive to bees," said Tsvetkov.

In lab studies that replicated the typical exposure scenarios they observed in the field — in terms of both pesticide duration and concentration — Tsvetkov and her colleagues found that worker bees exposed to neonicotinoids exhibited lower life expectancies, by up to 23 percent. Also, their colonies were more likely to permanently lose queens. "And," added Zayed, "their flights got progressively longer and longer as they aged, as if they were having a hard time finding food, or their way home."

Taken together, the research efforts in Canada and Europe show that neonicotinoids used in field conditions have real impacts.

"These studies show that concerns over neonicotinoid use and bee health are valid," Zayed said, "and they should be taken into account when re-assessing the safety of these agrochemicals in North America."

Kerr noted that despite the evidence these studies gathered, "We don't know for certain that [bees] will be harmed by a particular neonicotinoid application, but there is a pretty significant risk."

[Credit for associated image: Amro Zayed, York University]