Sen. James Inhofe made misleading claims in a letter to the Environmental Protection Agency about the relationship between neonicotinoid pesticides and bees:
- Inhofe said many scientists have concluded “that neonicotinoid pesticides only harm bees at dosages that are unrealistically high.” Actually, studies have shown that field-realistic doses of neonics can harm individual bees by inhibiting their immune system and navigation skills, among other effects.
- Inhofe said there is consensus “that multiple factors are related to honey bee losses.” That’s true, but Inhofe ignored that researchers stress interactions among factors, e.g. neonics can lower a bee’s immune system, making it more susceptible to viruses, which can then cause death.
Declines in honeybee populations across the U.S. and Europe have occurred since at least 2006. Pesticides, neonics in particular, have been targeted as one contributing factor. Others factors include disease, parasites, climate change, monoculture farming and habitat loss.
Inhofe, chairman of the Senate Committee on Environment and Public Works, made his remarks in a March 23 letter, which aimed to express his “interest and concern with a series of risk assessments” being conducted by the EPA on the effects of four types of neonics on bees, primarily Apis mellifera, a species of honeybee. First used in the 1990s, neonics are one of the most popularly used groups of insecticides in the world.
The EPA released its preliminary assessment of the neonic imidacloprid on Jan. 6 and is set to release preliminary assessments of clothianidin, thiamethoxam and dinotefuran in December 2016. Among other things, the first assessment indicated that “imidacloprid potentially poses risk to hives when the pesticide comes in contact with certain crops that attract pollinators.”
In his letter, Inhofe pressed the EPA to “establish a clear causal link” between neonics and bee population declines to “avoid repeating the mistakes” made by the European Union. But some scientists say it may be impossible to establish a clear causal link for honeybees in particular, given their large foraging ranges and other factors.
Instead of confirming a clear causal link, the EU applied the “precautionary principle” when it issued a moratorium on thiamethoxam, clothianidin and imidacloprid on Dec. 1, 2013, because information about their effects on bees is limited.
The EU’s temporary ban came after an assessment of the neonics by the European Food Safety Authority. Though the EFSA did identify “high acute risks” to bees associated with certain applications of neonics, it also acknowledged “data gaps” for certain crops. The moratorium since has been partially lifted in the U.K. following protests by farmers, according to the BBC.
We take no position on whether or not the EPA should follow in the EU’s footsteps and ban neonics. But we can say many scientists claim neonics do harm bees even at very low doses and may contribute to population declines. However, we stress that much still remains unknown about the cause of bee population declines.
In the next few sections, we’ll provide some background on bee population declines and neonic use. We’ll also outline what is presently known about the relationship between these two phenomena.
Bee Demise and Neonic Rise
According to the EPA, honeybee keepers began reporting “unusually high losses of 30-90 percent of their hives” during the winter of 2006 to 2007. Since then, the number of hives that don’t survive the winter – “the overall indicator for bee health,” says the EPA – has averaged about 28.7 percent per year. However, the loss dropped to 23.1 percent for the 2014 to 2015 winter.
Bumblebees have also declined in the United States and Europe, though this trend appears to have begun earlier in both cases. Little is known about solitary bees, which are bees that don’t live in a hive.
In total, 4,000 species of bees are native to the United States, according to the U.S. Department of Agriculture. However, the honeybee, the most commonly studied species with relation to neonics, is native to Europe, Asia and Africa. It was first introduced to North America in the 1600s. Today the honeybee is widely used for crop pollination and honey production across the U.S. and the world.
A particular type of decline seems to afflict honeybees. Colony Collapse Disorder (CCD) “occurs when the majority of worker bees in a colony disappear and leave behind a queen, plenty of food and a few nurse bees to care for the remaining immature bees and the queen,” explains the EPA. “While winter losses remain somewhat high, the number of those losses attributed to CCD has dropped from roughly 60 percent of total hives lost in 2008 to 31.1 percent in 2013.”
The EPA cites multiple, interacting factors as contributing to CCD, from parasites like the varroa mite to pesticides.
In total, 161 pesticides have been found in bee hives as of 2014. According to an April 2014 PLOS ONE paper by Francisco Sanchez-Bayo and Koichi Goka, bee experts at the University of Sydney in Australia and the National Institute for Environmental Studies in Japan respectively, three neonics — clothianidin, thiamethoxam and imidacloprid – are among the pesticides that pose the largest risks to honeybees based on exposure.
First commercialized in the early 1990s, neonics are now used in more than 120 countries. They became one of the most, if not the most, popularly used insecticides worldwide because they target invertebrates, like insects, rather than vertebrates, such as birds and humans. Similar in chemical structure to nicotine, neonics act as neurotoxins for invertebrates, which means they cause paralysis and ultimately death in insects.
Neonics are commonly applied as seed coatings, though they can also be applied in other ways, including directly to the soil. As the crop grows, the insecticide spreads through the plant’s tissues, pollen and nectar. Then, when a pest eats the plant, it ingests the insecticide and dies. Since neonics are water-soluble and degrade slowly, they can remain in the soil or in treated plants for months — even years — after an application.
At high enough doses, neonics can directly lead to death in bees. This is undisputed. Exposure to higher doses can occur when dust is stirred up during planting of the coated seeds, for example.
Of more concern is their chronic, sub-lethal exposure to neonics via nectar, pollen and water expelled from plants through a process called guttation.
In the next section, we’ll outline the evidence that counters Inhofe’s claim that “neonicotinoid pesticides only harm bees at dosages that are unrealistically high.”
Realistic Doses Harm Bees
Studies published in Science and other journals have shown that field-realistic doses of neonics can harm various bee species. In fact, two Science studies published on April 20, 2012, spurred the EFSA’s assessment of three neonics in 2013, which ultimately led to the EU’s moratorium on the pesticides.
In one Science study, Dave Goulson, a bee expert at the University of Sussex in the U.K., and others exposed bumblebees to “field-realistic” levels of imidacloprid in the lab and then released them “to develop naturally under field conditions.” The group found that “[t]reated colonies had a significantly reduced growth rate and suffered an 85% reduction in production of new queens compared with” untreated colonies.
In the second Science study, a group of researchers including Mickaël Henry, a bee expert at the French National Institute for Agricultural Research, exposed honeybees to field-realistic doses of thiamethoxam. They then attached miniature radio-frequency devices to the backs of 653 bees and found that a honeybee forager would be up to twice as likely to “die because of homing failure during a day spent foraging on treated crops” than to die naturally that day.
The researchers also used population dynamic models to assess how much these mortality rates due to decreased navigation skills might affect the hive as a whole. They found “populations from colonies exposed to the treated nectar would follow a marked decline during [April to May] and would hardly recover afterward.”
Another study by Francesco Pennacchio, a bee expert at the University of Naples Federico II in Italy, and others found that field-realistic doses of the neonic clothianidin can suppress the honeybee’s immune system by disrupting a molecular pathway that plays a key role in regulating the insect’s response to infection. Published in Proceedings of the National Academy of Sciences on Oct. 21, 2013, the paper describes a “causal link” between clothianidin and harm to a bee’s immune system.
To be clear, these studies do not, by scientists’ standards, confirm a clear causal link between bee population decline and neonics – which is what Inhofe is asking of the EPA. But they do provide evidence that neonics can harm bees, even at very low doses, contrary to Inhofe’s claim.
Limits of Bee Research
When we asked Kristina Baum, press secretary for the Committee on Environment and Public Works, what a “clear causal link” between neonics and bee population declines would entail by Inhofe’s standards, she told us that “Inhofe is referring to results from studies that look at actual exposure of bees to neonicotinoids in the field.”
A team in Sweden has performed a field experiment on bumblebees and honeybees. Published in Nature on May 7, 2015, the study by Maj Rundlöf, a bee expert at Lund University, and others found that oilseed rape seed coating with Elado, an insecticide containing clothianidin and another nonsystemic chemical, reduced “bumblebee colony growth and reproduction” under replicated field conditions.
However, they found that “the insecticide seed treatment had no significant influence on honey bee colony strength.” While the researchers quantified colony growth as the weight of the bumblebee hive, they quantified colony strength as the number of adult bees.
The Nature paper cites research that suggests honeybee colonies may be better at detoxifying after exposure to neonics compared with bumblebees – evidence that it may not be possible to extrapolate honeybee colony and population level data to other bee species.
Goulson, with the University of Sussex, told us he was less convinced by Rundlöf et al.’s findings on honeybees than their results on bumblebees. The Nature study used sites with a 2 kilometer radius, which may not account for the honeybees’ extensive foraging range, he said.
While honeybees have been shown to forage around 6 kilometers from their hives, bumblebees appear to normally stay within 1 kilometer of their hives. Thus, researchers can’t control field experiments on honeybees as easily as those on bumblebees, Goulson told us.
To be clear, Rundlöf and her coauthors don’t believe their study alone is enough to confirm a clear causal link between bee population decline and realistic neonic use.
Like Goulson, Rundlöf also told us that “it would be very hard, if not impossible, to conduct an experiment that would establish a clear causal link between real neonicotinoid use and bee population decline.”
In order to establish a clear causal link between field realistic doses of neonics and bee population declines, scientists would have to monitor and control countless variables including how different bee species respond to different neonics pesticides, which are applied to different crops in different doses and in different landscapes.
Thus, Inhofe may be holding scientists to too high of a standard when he pressed the EPA to “establish a clear causal link” between neonics and bee population decline, given the difficulty of performing experiments in the field, especially on honeybees.
Even if much remains unknown, scientists are certain that the cause of bee population declines involves multiple and interacting factors. In the next section, we’ll outline the evidence that backs up this theory.
Multiple AND Interacting Factors
In his letter, Inhofe cites a newspaper commentary piece to support his claim that many scientists have come “to the conclusion that neonicotinoid pesticides only harm bees at dosages that are unrealistically high and are unlikely the cause for the decline in bee populations.” The commentary by beekeeper Peter Borst, published in Albany, New York’s Times Union in February, states: “Various scientists, including Marla Spivak of the University of Minnesota; Walter Sheppard of Washington State University; and Richard Fell of Virginia Tech affirm that neonics are not a significant driver of honey bee decline.”
We reached out to all of these scientists, but only Fell responded. He told us by email that Inhofe’s claim is “partially correct” (what we call misleading) because “there is no evidence that field-realistic neonicotinoid exposure is directly involved in honey bee colony losses, and as such, are unlikely to be ‘the cause’ of honey bee decline.”
But he added, “[t]his is not to say that field-realistic doses couldn’t contribute to colony weakening, and hence losses due to environmental stress, diseases, parasites etc.”
In other words, neonics are unlikely a direct and primary cause of bee population declines, but their interaction with other factors like disease and parasites could impact bees at the colony level. Marla Spivak makes similar claims in her Ted Talk, “Why bees are disappearing.”
For instance, Pennacchio’s PNAS study cited above showed that by suppressing the honeybee’s immune system, field-realistic exposure to clothianidin promoted “replication of a viral pathogen in honey bees.”
In a Science review published on March 27, 2015, Goulson and colleagues also stressed the impact that exposure to multiple pesticides has on bees. For example, they write, some fungicides “have very low toxicity in themselves but may increase the toxicity of some neonicotinoids and pyrethroids by as much as a factor of 1000.”
A March 2010 Environmental Microbiology study, conducted by Yves Le Conte and others at the French National Institute for Agricultural Research, also found that the combined presence of the parasite Nosema and imidacloprid led to higher mortality rates in honeybees than one factor or the other on its own. The researchers found this effect at very low doses of imidacloprid, though it was more pronounced at higher doses.
Goulson’s Science review also mentioned that the neonic-induced decreased foraging abilities noted above in honeybees and bumblebees could also exacerbate “nutritional stresses,” which, in turn, could inhibit a bee’s ability to “cope with pesticides,” in a cycle.
Nutritional stresses can also come from habitat loss, one factor that Spivak does argue could play a major role in bee population decline in her Ted Talk. Goulson et al. noted in Science that the “conversion of natural and seminatural flower-rich habitat to farmland has been a major driver of long-term declines in bees.”
The review also mentioned the difficulty in successfully conducting studies on these multiple and interacting factors, but said “a strong argument can be made that it is the interaction among parasites, pesticides, and diet that lies at the heart of current bee health problems.”
To sum up, Inhofe was misleading when he claimed that many scientists have concluded “that neonicotinoid pesticides only harm bees at dosages that are unrealistically high.” Field-realistic doses of neonics can harm bee individuals. While it’s unlikely that neonics are the sole or primary factor causing bee population decline, much is still unknown about the exact mechanisms underlying the decrease. Bumblebee populations do appear to suffer losses from realistic doses, based on the available evidence. Scientists don’t have a clear causal explanation for honeybee population decline, but they know it involves multiple, interacting factors.
Editor’s Note: SciCheck is made possible by a grant from the Stanton Foundation.
Clarification, April 25: We changed one word of this story to make clear that bees can be exposed to higher doses of neonics during planting of coated seeds, as opposed to afterward.