Environment

Are Pesticides Called Neonics to Blame for the World’s Bees Crisis?

Neonicotinoids, popularly called neonics, came on the scene when other pesticides no longer deterred pests but instead poisoned vertebrates.

Eastern bumblebee, <em>Bombus impatiens</em>, pollinating lupine flowers in Canada. Neonics hamper the reproduction of such bees. Credit: Jeremy T. Kerr

Eastern bumblebee, Bombus impatiens, pollinating lupine flowers in Canada. Neonics hamper the reproduction of such bees. Credit: Jeremy T. Kerr

Update, August 14: Unlike honey bees that are active throughout the year, bumblebees hibernate through winter. After they emerge in spring, bumblebee queens work alone to start colonies. Emaciated from the long sleep, they may be additionally stressed by neonicotinoid pesticides.

Scientists from the UK and Canada investigated the effects of these chemicals on bumblebee queens in a paper published in the journal Nature Ecology & Evolution. Eating nectar and pollen contaminated with thiamethoxam, a neonic, for two weeks was enough for 26% of the queens to stop laying eggs. Mathematical modelling showed that, at this rate, populations could drop steeply, leading to local extinctions. The researchers suggest the insects may shunt nutrients to metabolising the toxins rather than reproduction.

Stronger queens overcame the stress of pesticide poisoning by laying eggs earlier than normal. Such early-born young may emerge before peak flowering season and may not get enough to eat. They’d also miss opportunities for mating if the rest of their generation were to hatch at the normal time. Unaffected vigorous queens laid many more eggs.


July 23: Blame for the decade-long crisis in the honeybee industry is often pinned on pesticides. Several studies correlate the two, but the smoking gun was elusive. Now two studies that address the criticisms of earlier studies offer a troubling picture.

Neonicotinoids, a new generation of pesticides, have been around since Shell developed them in the 1980s and Bayer began production in the 1990s. They are now the most commonly used insecticides. Until then, from the 1960s to the early 1990s, farmers sprayed organophosphates and organochlorines repeatedly during a crop’s lifetime to kill agricultural pests. These are the same chemicals that Rachel Carson decried in her book Silent Spring for contaminating soil and water, and affecting fish, birds, and humans.

Neonicotinoids, popularly called neonics, came on the scene when pesticides no longer deterred pests but instead  poisoned vertebrates. The most widespread use of neonics is to coat seeds, but they are also sprayed on plants, applied on soil or injected in tree trunks. Absorbed by roots and leaves, they turn whole plants toxic for weeks. Even at low concentrations, their long life meant they didn’t have to be applied repeatedly. The good news: they were deadly for insects without harming birds, livestock and humans. (In later studies, seed-eating birds like partridges fell dead after eating treated seeds.) Aphids sucking plant juices and beetles munching on leaves get poisoned with every mouthful. Neonics affect the central nervous system of invertebrates, binding to their postsynaptic nicotinic acetylcholine receptors.

Ten thousand times more toxic than DDT, they cause rapid paralysis and death. A mere four nanograms of clothianidin, the most commonly used neonicotinoid, kills half of all the honeybees that feed on it. In real world terms, a bee has to only eat one gram of pollen or 2.6 millilitres of nectar from treated plants to reach this threshold. And while organophosphates degrade quickly, neonics last months, even years, in soil and groundwater.

Colony collapse disorder

During the winter of 2006, reports of a worrying trend called colony collapse disorder surfaced in the US. Whole colonies of worker bees vanished, leaving hives with queens, brood and adequate food stocks. Normal worker bees wouldn’t abandon such productive hives, and without their tending, colonies cannot survive. European bee hives suffered to a lesser degree. The resulting losses didn’t hit the honey industry alone. Missing insect pollinators severely dents agricultural productivity, causing an estimated loss of $200 billion a year globally. 

In several countries, the disappearance of honeybees coincided with the increasing use of seeds coated with neonics.

One study said thiamethoxam, a neonic pesticide, garbled honeybees’ navigation skills so they couldn’t find their way back to their hives. Another showed imidacloprid, also a neonic, stunted the growth of bumblebees and suppressed their ability to produce queens. Using 18 years of data, a third study study implicated neonics in the disappearance of many populations of the UK’s wild bees. Conversely, a few studies found neonics didn’t affect honeybees or bumble bees. Yet another study found that oilseed rape or canola, a mustard relative, treated with clothianidin was more toxic to wild bees than honeybees.

Despite this mixed bag of results, governments have been forced to act.

Chemically coated seeds absorb moisture and become sticky. To move them smoothly through planters, farmers mix them with talc and graphite. But these neonic-tainted lubricants became airborne when farmers handle the seeds. The Canadian government concluded that this dust had caused most of the bee mortality through spring and summer of 2012 in Ontario and Quebec. It demanded that farmers use a specific wax-based seed fluency agent, instead of talc and graphite, to reduce air contamination.

Across the Atlantic, in 2013, the European Union (EU) temporarily banned the use of three neonics on flowering crops. Pesticide companies argued the chemicals didn’t cause harm and were needed to control pests and increase food production. The UN, in reply, called that a myth. In March this year, The Guardian reported that the EU was considering a complete ban on the use of neonics in agriculture. If a majority of member countries vote for it, it could become operational this year itself.

Most research so far has focused on the effects of neonics on a few hives, leading to criticisms of study design flaws. The researchers were said to have fed high doses of pesticides for too long to bees in experiments. Now, two studies from Europe and Canada have investigated if neonics badly affected bees under natural conditions in the fields.

The European study

Bombus rufocinctus, the red-belted bumblebee, covered in pollen while visiting a chive flower in Ottawa, Canada. Credit: Jeremy T. Kerr

Bombus rufocinctus, the red-belted bumblebee, covered in pollen while visiting a chive flower in Ottawa, Canada. Credit: Jeremy T. Kerr

The authors examined the effects of pesticides on hives across entire landscapes, taking into account land use, regional climate and two insecticide formulations. They chose 33 canola-growing sites in three countries: Hungary, Germany and the UK.

“We designed a robust study at real world scales which allowed us to identify what occurs where bees are exposed to real world conditions which are inherently very variable,” Ben Woodcock, the lead author, at Centre for Ecology and Hydrology, Oxford, told The Wire. “This is one of the things that makes this such an important study.”

Although funded by Syngenta and Bayer, companies that produce neonics, the authors had “independence to analyse and interpret the results” as they saw fit. “We were able to put in place checks to ensure independence,” says Woodcock. “For example, independent oversight groups of top academics, publishing all protocols online and maintaining transparency through the publication of raw data with the paper. Obviously, there were concerns from outside that our results may be influenced. However, we believe that our interpretation of the data has been robust, fair and accurately reflects real world impact of neonicotinoids on bees.”

The oilseed is sown in August and harvested by July or August the following year. Study sites used Bayer’s clothianidin or Syngenta’s thiamethoxam. Some used no neonics and acted as the control. (Researchers compare the results of an experiment with a situation, or control, that is similar in every way except it doesn’t receive the treatment – in this case, of neonics.) The researchers had to obtain permission to use these pesticides for the study. At each site, they introduced colonies of honeybees, wild buff-tailed bumblebees and solitary mason bees.

Bee populations in the three countries reacted differently. Neonics suppressed reproduction in Hungary but didn’t make a difference in Germany. Few workers survived through winter in Hungary while more did in Germany. In the UK, honeybees had a tough time living through winter, and clothianidin made matters worse. In summary, German honeybees seemed to be made of sterner stuff than Hungarian ones while British honeybees were the worst off.

Why did the same species fare differently against the same chemicals in different countries? The answer is resilience. Honeybees in the larger and healthier German hives relied on the flowers of oilseed rape for only 15% of their diet. They buzzed on neonic-free wild flowers for the rest. However, in Hungary and the UK, disease stressed the colonies. And the bees had few other foraging options, depending on the crop for nearly half their food needs. When these already beleaguered honey bees were also forced to deal with neonics, they did poorly.

“In the same way that if someone is weak and malnourished they are more susceptible to getting a disease, the same thing happens with honeybees,” says Woodcock. “Where they have high levels of disease (e.g. Varroa mites) or are forced to feed on a poor diet dominated by oilseed rape as there are few other flowering plants in the landscape then they experience negative effects of neonicotinoids.”

Neonics weren’t kind to wild bees in any of the three countries. Reproduction of buff-tailed bumblebees and mason bees suffered, not only because of neonics used during the study but from an entirely different source. Their nests had residues of imidacloprid, a pesticide that wasn’t used in the study, and the authors say its presence indicates the contamination of the wider landscape before the EU moratorium had taken effect.

“This is by far the largest field trial ever conducted on the impacts of neonicotinoids on bees, including honeybees, bumblebees and solitary bees, and conducted simultaneously across the UK, Germany and Hungary,” says David Goulson, a professor of biology at the University of Sussex, UK. “The findings are in agreement with a number of earlier studies – field exposure to neonicotinoids has clear negative impacts on bumblebees and solitary bees.” Goulson was not involved in the study.

“Because we did not find consistent effects of neonicotinoids everywhere it suggests that there may be approaches to mitigate their use at a reduced level,” says Woodcock. “The establishment of high-quality flower and nesting resources for bees in agricultural landscapes and new approaches to improving honeybee health may provide opportunities to continue to use these pesticides. However, this is something that would need to be tested, as we only infer this from the results of our study.”

The Canadian study

Another field study in Canada came to similar conclusions. Researchers in Ontario and Quebec found the presence of 26 agrochemicals, including neonics, in honeybee hives near maize fields. Although these insects didn’t forage in croplands, neonics had found their way into the hives.

“When we analysed the pollen samples that contained neonicotinoids, we found that the majority of the pollen came from plants such as willow and clover,” Nadia Tsvetkov, the lead author from York University, Canada, told The Wire. “Neonicotinoids are water-soluble, so when it rains, the pesticides get into the soil where they get absorbed by the surrounding plants.”

Despite Canadian regulations to cut down pesticide-tainted dust, neonics had spilt over from farmlands into the countryside.

By affixing radio frequency identity tags to bees, the researchers followed their individual fates. The lifespan of clothianidin-treated bees was cut short by five days (a reduction of 23%) compared to controls that lived approximately for three weeks. And as long as they lived, the impaired bees didn’t perform their normal duties such as housekeeping; they ignored the dead and sick brood instead of removing them from the hives.

“Our control and exposed colonies started in the same condition and were treated the same, with the exception of clothianidin addition to the exposed colonies,” says Tsvetkov. “We saw that clothianidin treated colonies had reduced hygiene behaviour as a factor of time, meaning the longer they were exposed, the less hygienic they were.”

The researchers say this indicates an impaired social immune system, since the lack of care affects the health of the colony.

Neonics are frequently used along with other chemicals such as herbicides and fungicides. The herbicide linuron and fungicide boscalid don’t cause mortality by themselves. But they made neonics almost twice as toxic to honeybees, say the researchers.

The exposure of honeybees to neonics wasn’t brief enough to be ignored. They fed on contaminated wild pollen and nectar every day for four months, through spring and summer.

“In the light of these new studies, continuing to claim that use of neonicotinoids in farming does not harm bees is no longer a tenable position,” says Goulson. “In my view, we should also consider the bigger picture – the current model of farming based on huge monocultures treated with dozens of pesticides is causing devastating environmental harm, undermining vital ecosystem services that keep us all alive. Simply banning neonics and replacing them with some other toxin will not solve the problem.”

In India

Anecdotal reports indicate all is not well with Indian bees. How badly are they affected? No study has yet assessed the true scale of decline. However, farmers in Odisha have reported a drastic decline in crop yields related to a lack of pollinators over the last couple of decades.

In a May 2016 report, Arati Pannure of the University of Agricultural Sciences, Bengaluru, quoted another study that claimed honeybee numbers fell 40% over 25 years. But this study’s supplementary data couldn’t be verified.

Most crops in India are pollinated by wild bees and we know nothing about how they fare. In the Nilgris, Tamil Nadu, indigenous communities that harvest honey from wild hives have reported a massive decline in yield. Similarly, in 2011, wild honey collection fell from 300 tonnes to 50 tonnes in Kutch.

Are the same pesticides the culprits? According to the recent studies from Europe and Canada, they could well be. In 2014, the Indian government considered a ban on the neonic pesticide called imidacloprid – but this has remained just a news report.

The Canadian and European studies were published in the journal Science on June 30, 2017.

Janaki Lenin is the author of My Husband and Other Animals. She lives in a forest with snake-man Rom Whitaker and tweets at @janakilenin.