French Researchers Solve Discrepancy in Bee-Killing Neonic Studies

Washington, DC–(ENEWSPF)–November 20, 2015.  French scientists say that they have found the “missing link” between laboratory studies and field studies that assess the adverse effects of neonicotinoid (neonic) insecticides on bees. The study, published in Royal Society Journal Proceedings B, evaluates the effects of neonics on honey bees in field trials. After 15 years of research into the effects of neonicotinoids on bees, researchers had identified a gap between the results of toxicity assessments on individual bees in the laboratory and  impacts seen at the colony level in the field. The new two-year study made two discoveries: First, they found that field exposure to thiamethoxam combined with imidacloprid contamination is associated with a significant excess mortality in individual free-ranging bees. Second, while colonies appeared to be able to compensate for the excess mortality and preserve population size and honey production, this was done at the expense of a change in brood laying patterns. Thus, this study provides an explanation for the “missing link” in the discrepancies between labs studies and field studies, where the former establishes harmful and fatal effects that had yet to be replicated in real-life conditions. Because the bees responded to the increased mortality with selective population regulation, the proportion of male bees declined significantly, representing an abnormality with potentially widespread impacts for the health of honey bee colonies

Researchers found that “there was a change in the way reproductive effort was allocated between female (worker) brood and drone (male disperser) brood. During flowering, the most exposed colonies tended to invest more in worker brood production at the expense of drone brood production. Drones are more costly to produce and maintain than workers, among others because they do not participate to the foraging task force.” Because male drone bees are only necessary for mating, their decreased population proportion is temporarily beneficial for maintaining honey flow, yet detrimental to long-term colony sustainability. A study led by Geoff Williams, MD, Ph.D, at the University of Bern in Switzerland found that queens exposed to noenics were more likely to not lay worker eggs, a key indicator of queen health and mating success. In light of this recent study, it may be inferred that individual bee mortality due to neonicotinoid insecticides results in an adverse positive feedback response from the queen that causes detrimental effects on the long-term success of the colony.

Christopher Connolly, Ph.D. of the University of Dundee explained that, “It is important to remember that all other insect pollinators do not possess the enormous buffering capacity of honeybees and are therefore more acutely at risk to the impact of pesticides.” He also said that the study identifies, “

The French scientists had to obtain special permission from the French Food Safety Agency, ANSES, to use rape (canola) seeds treated with thiamethoxam; their use is currently prohibited on flowering crops within the European Union. “These systemic insecticides,” explains the scientists, “which now represent about 30% of insecticide use worldwide, pose a particular risk for pollinators, because once the active substance has been taken up in the plant, its residues translocate to the pollen and nectar collected by foragers throughout flowering.”

In addition to thiamethoxam, researchers discovered an unexpected and substantial concomitant exposure to imidacloprid at residue levels high enough to adversely affect bees. In France, this neonic is still currently used to treat seeds for crops such as wheat, barley, and sugar beet, but had not been used on rapeseed. In January, imidacloprid was found to cause mitochondrial dysfunction in bumble bees, which then negatively impacts navigation and foraging skills. The contamination of imidacloprid in current study where it was not purposefully applied points to its ability to persist in nature for long periods of time. That persistence not only exposes bees to the harmful effects of imidacloprid alone, but also a potentially synergistic combination of neonics that have unknown effects. The discovery of this chemical in the nectar of rapeseed crops concurs with the substantial re-uptake of neonicotinoid residues recently reported in pollen and nectar samples from wild flowers in field margins (where wild flowers at sometimes contained even higher concentrations than in the flowering crop itself).

Scientists concluded that “more detailed studies on the environmental fate of neonicotinoid residues are urgently needed to properly control for potential confounding effects or synergistic effects between different active substances.” While this statement speaks to the need for more studies to determine specific mechanisms regarding how neonics impact pollinators, it also gives weight to existing studies showing significant harm. In 2013, scientists at Royal Holloway University of London determined that low-level exposure to imidacloprid causes chronic sublethal stressors that lead to colony collapse. That year, a study by David Goulson, Ph.D, of the University of Sussex, also found that the soil half-life of the most commonly used seed treatments can range from 200-1000 days, resulting in  wide ranging ecological damage.

In the U.S., action at the federal level has done little to take the sting out of pollinator declines. Despite the announcement of a coordinated National Pollinator Health Strategy this May, federal agencies continue to exhibit widely different approaches on how to address pollinator declines. While the U.S. Fish and Wildlife Service banned the use of neonics on National Wildlife Refuge Land, and the White House Council on Environmental Quality released new guidelines prohibiting the planting of neonic-treated plants at federal facilities, EPA and U.S. Department of Agriculture (USDA) have taken little substantive action. Although EPA recently proposed modest label changes to protect bees from acute pesticide exposure, USDA submitted comments criticizing the agency’s proposed rule, saying that it had “not established the need for such a prohibition.” In fact, USDA has gone as far as suppressing and targeting its own scientists that have linked neonics to bee-toxic effects.

The Saving America’s Pollinator’s Act of 2015 remains an avenue for Congress to address the pollinator crisis. Contact your U.S. Representative and ask them to support this important legislation today. You can also get active in your community to protect bees by advocating for policies that restrict their use. Montgomery County, Maryland recently restricted the use of a wide range of pesticides, including neonics, on public and private property. Sign here if you’d like to see your community do the same!

All unattributed positions and opinions in this piece are those of Beyond Pesticides.

Sources: The Royal Society: Proceedings B,