Going against studies showing that neonicotinoid pesticides harm bees, Bayer has routinely defended itself by pointing out that the data was gathered under artificial conditions – by force-feeding bees in a lab, rather than by studying them out in the field. Bayer states on its website that “no adverse effects to bee colonies were ever observed in field studies at field-realistic exposure conditions.” But a large study now makes it harder for Bayer to claim that defense. 
In late June 2017, two studies in the prestigious journal Science revealed results from the largest field studies to date on neonicotinoid pesticides (most commonly applied to corn and soybean seeds) and their effects on bees.
Study #1 Yields Some Interesting and Unexpected Results
In the first study – funded in part by Bayer and another neonicotinoid (‘neonic’) manufacturer, Syngenta – researchers monitored honeybees and 2 types of wild bees at 33 sites across Europe: in the United Kingdom, Germany, and Hungary. The bees were placed either near canola fields grown from seeds treated with neonics, as well as with a standard fungicide, or near canola fields planted with untreated seeds.
It found that at most sites, bees that fed on neonic-treated canola fields were by far unhealthier than bees who fed on untreated fields. This was found to be especially true of bees feeding at the sites in Hungary and in the U.K. The bees that were exposed to neonics had trouble reproducing, and fewer honeybee colonies survived the winter.
Lead researcher Richard Pywell, from the Centre for Ecology & Hydrology in the U.K., said the findings were “cause for concern.”
However, the results were far different in Germany. Honeybee colonies appeared to do exceedingly well, despite being treated with pesticides. In Germany, honeybee colonies located near fields treated with neonics produced more eggs, and more larvae. Although fewer colonies survived the winter, the difference was statistically insignificant.
“We think this is a really interesting result… We believe that other factors interact with neonicotinoid exposure to cause negative effects on honeybees and wild bees.” 
The scientists aren’t sure what those other factors might be, but they have some clues. More on that later.
Neonic Toxicity Heightens When Combined With Other Chemicals
Neonics dissolve in water and easily work their way into waterways via agricultural run-off. The chemicals can seep into the stems, leaves, pollen, and nectar of flowers grown miles away from treated sites.
So in the second study, researchers investigated agricultural chemical use near Canadian cornfields grown from neonicotinoid-treated seeds. Amro Zayed, a biologist at York University in Toronto, and a team of colleagues looked for the presence of neonics on dead bees, forager bees, nurse bees, larvae, pollen, and in nectar. 
The researchers discovered the presence of a mixture of herbicides, fungicides, and pesticides, including neonicotinoids. The majority of the neonics that the team found were detected on pollen from plants other than corn, including willow trees, clovers, and wildflowers, located near treated crops.
Ecologists previously believed that bees were only exposed to the pesticides when near a treated, flowering crop – but the study showed that the pesticides persist throughout the whole growing season. This means that bees are vulnerable to the chemicals even when a crop is not in bloom.
Zayed and his team carried out their experiments in an outdoor lab, far from crop fields. They exposed bees to clothianidin – one of the most commonly used neonicotinoid pesticides at Canadian farms – over a 12-week period, at the same levels encountered near farms. Each exposure involved smaller and smaller amounts of pesticide to simulate rain washing away the compound in nature.
Worker bees in the lab lived 3/4 as long as those near farms, and clothianidin impaired the insects’ natural defense systems. Bees use a tactic called “social immunity” – cleaning out dead or sick broods from the nest to avoid illness. Bees in the colonies treated with clothianidin displayed less and less of this behavior over time – sick bees remained in the nest and infected the healthy bees.
The scientists observed something similar in the cornfields the year before. By the end of the growing season, bee hives near the fields displayed less social immunity behavior than colonies far away from the fields.
Additionally, the tainted hives tended to lose their queen and had trouble finding a replacement. Without a queen, there are no eggs or future bees.
And when Zayad’s team tested herbicides and fungicides on the bees, neither the most common herbicide (linuron) nor the most common pesticide (boscalid) killed the bees – at least not on their own. But combined with clothianidin, it took half as much of the chemicals to kill as many bees. The same rang true when clothianidin was swapped with the neonicotinoid thiamethoxam.
Why Such a Mixture of Results? “Other Factors.”
So what caused such mixed results in the first study? There are a number of factors that scientists think are at play.
For example, honeybees in Germany fed on a wider variety of flowers than those in the U.K. and Hungary. In those countries, 40-50% of the pollen collected from honeybees was from canola, compared to just 10% in Germany.
Pywell explained that the bees in Germany were surrounded by enormous canola fields. However, in the U.K., “because of modern farming, we’ve lost many of our wildflowers, so the crops are pretty much all that’s there in the springtime.” 
Additionally, parasites were a problem for the honeybees in the U.K. and Hungary, but most of the bees in Germany were parasite-free.
Pywell believes that bees become more susceptible to neonicotinoids when they’re highly dependent on pesticide-treated crops for food, and when they are already weakened by disease.
Jeffrey Donald, a spokesman for Bayer, wrote in an e-mail that “the study shows when hives are healthy and relatively disease-free, and when bees have access to diverse forage, neonics do not pose a danger to colony health.”
Maybe not, but the results show that when mixed with any one of the many noxious chemicals made by the biotech industry and applied by farmers, neonics can be deadly to bee populations.
 PBS Newshour