One of the world's largest field studies tests bee safety

Rapeseed: A safe source of food?

Large rapeseed fields are an important source of food for bees. Unfortunately, pests which weaken the plants and diminish flowering potential, consequently, also threaten this important resource for bees. Available crop protection products for controlling some rapeseed pests are limited. The registration for a highly effective product was withdrawn due to concerns that rapeseed grown from seed treated with the product might harm bees. In order to generate additional real-field evidence, Bayer investigated the safety of these products to pollinators using rapeseed grown from clothianidin-treated seed.

One of the world's largest field studies tests bee safety


// There is intensive scientific discussion as to whether or not neonicotinoids harm bees.

// Bayer commissioned one of the largest field studies of rapeseed in the world. In total, some 1,400 hectares of agricultural land, equivalent to roughly 4 times New York Central Park, was sown.

// The company and agricultural experts of other institutions jointly investigated whether plants grown from seeds treated with clothianidin had an effect on wild bees and honey bees.

// For the three bee species observed, experts did not find any evidence of harmful effects from the seed treatment.

Rapeseed is particularly attractive to bees, because the crop produces abundant amounts of nectar. Additionally, its pollen supplies essential amino acids and proteins which the bees need to raise their brood. However, when worker bees forage on crops that have been seed-treated with systemic pesticides, there is a chance that they collect small amounts of these substances with the nectar and pollen from the flowers. Small amounts of these substances are harmless to bee colonies. In recent years, however, there has been growing concern by some stakeholders that even traces of crop protection products known as neonicotinoids could be harmful to the health of honey bees and other pollinators.

Rapeseed field

In the midst of activities: Dr Fred Heimbach (above) coordinated the study and brought all participants together.

In 2013, the European Commission responded to these concerns by asking the European Food Safety Authority (EFSA) to carry out a review of the safety of neonicotinoid seed treatment products. EFSA analyzed the results of previously submitted registration trials, using new and extremely conservative criteria. As a precautionary measure, the EC restricted the use of three neonicotinoid substances in certain crops deemed attractive to bees.

This restriction has had consequences for farming: Pests destroy crops and need to be controlled. Jörg Thieß, the manager of Agrargenossenschaft Groß Niendorf e.G. in Germany, has experienced this situation firsthand. At first glance, his rapeseed field appears to be growing well – but a closer look reveals holes chewed through the leaves and eroded stems. Even the roots, well below the soil, are damaged. Pests – such as the pollen beetle, cabbage stem flea beetle and the cabbage root fly – weaken the plants and ultimately destroy large areas of the crops. “At this point, all we can do is accept the loss of yields within the rapeseed farming community,” Thieß says. A few years back, Thieß as well as other farmers had beenable to control the pests. However, with the new EU regulations, farmers are no longer permitted to use seed treatment products containing clothianidin, and effective alternatives are scarce.

Dr. Richard Schmuck

Environmental safety is the highest priority for Dr Richard Schmuck (below). His department evaluates Bayer’s plant protection products.

This leaves farmers in a predicament. Due to the restrictions, some now cultivate less rapeseed than before. “We have already reduced rapeseed yields by a third,” Thieß states. This not only decreases the production of rapeseed oil, animal feed and bio-diesel but it also eradicates valuable sources of forage for bees. “The question as to whether these restrictions make farming any safer for bees has been ignored,” says Dr Richard Schmuck, the director of Environmental Safety at Bayer. Dr Holger Kersten, an agricultural consultant for crop protection products, adds: “Only scientifically sound data will allow for objectivity within the debate on controversially discussed products.”

Therefore, Bayer initiated one of the world’s largest bee monitoring studies in rapeseed fields. The study’s participants included bee and crop protection experts as well as beekeepers and farmers in Mecklenburg-Western Pomerania (northeastern Germany). Their goal: To make a large-scale test on landscape level of the crop protection product Elado® – which contains the active substance clothianidin – under realistic agricultural conditions. Several farmers provided their agricultural land. They sowed rapeseed that had been pre-treated with clothianidin in 2013, the last year when the usage of the restricted neonicotinoids was allowed in winter rapeseed. This seed treatment process covers seeds with a thin multi-layer containing the crop protection product. It is through the roots, then, that the plant absorbs the substance that offers protection against destructive pests during germination and early growth. The farmers sowed these treated winter rapeseeds throughout a total of 800 hectares of agricultural land. On similarly large control fields, untreated rapeseed was cultivated. “The farmers were left to cultivate their fields using their own normal farming practices,” explains Dr Fred Heimbach, Senior Expert Ecotoxicology at tier3 solutions and coordinator of the study. “This allowed the researchers to conduct their field studies directly on typical locally cultivated fields, avoiding a simulated test design that would have limited practical relevance. The conditions were completely realistic,” states the ecotoxicologist.

Sebastian Wiegand and Daniel Rolke

Sebastian Wiegand (left) and Daniel Rolke (right), project leaders from the German Bee Research Institute in Oberursel, analyzed the health of the honey bee colonies being studied.

The bee health monitoring activities began in spring 2014, during the flowering period: Experts from the Bee Research Institute in Oberursel, Germany, positioned 96 honey beehives alongside rapeseed fields. In addition, two types of wild bee species were released: the buff-tailed bumble bee and the solitary red mason bee. Under these realistic conditions, the researchers wanted to determine any effect that the crop protection product might have on the different bee species. To provide the most accurate data, the trial and control fields were set far apart from each other, which would prevent the bees from moving between treated and untreated fields. To limit alternative sources of forage, the fields were carefully selected to ensure there were no other bee-attractive crops in the surroundings.

“The researchers did not observe any signs of harmful effects to the three bee species from the clothianidin-treated crop,” Dr Schmuck says. To assure that the bees did, in fact, forage on the treated rapeseed plants, the team of researchers monitored the pollen brought back to the beehives:

honey bees and bumble bees

During the study, honey bees (right) carry rapeseed pollen into their hive. The bumble bees (left) also bring their food into the bumble bee box.

“The foraging honey bees mainly collected food on the rapeseed fields,” Dr Heimbach recaps. The red mason bee and the buff-tailed bumble bee are known to collect pollen from different types of wild plants. In this study, the bumble bee also collected significant amounts of pollen from rapeseed plants on several occasions when measurements were being made. The researchers also examined the amount of residues from substances in pollen samples. The results: Clothianidin was only found in small amounts, at levels typical for winter rapeseed and below levels deemed harmful for bee colonies. “Many field trials from different groups of scientists have proven that crops which have been seedtreated with neonicotinoids do not harm the health of honey bees under realistic conditions,” says Dr Christian Maus, Global Pollinator Safety Manager at Bayer.

Martina Flörchinger

Precise observation: Martina Flörchinger, employee at tier3 solutions, counts the number of red mason bees in the nesting site.

The study confirms this; honey bees showed stable colony development and delivered good honey yields. Similar findings were observed for the other two bee species: The strength of the bumble bee colonies and the number of queens, drones and female workers were well comparable between control and treatment groups. The red mason bee also showed normal nesting and reproductive behavior. “It has become clear that seed treatment of rapeseed is not harmful to bees,” Dr Heimbach concludes.

While the honey bees near the treated rapeseed fields developed perfectly, a different stress factor caused trouble during the winter period: Large numbers of the tested colonies died due to the Varroa mite.
“Unfortunately, the infestation levels of honey bee colonies was too high to finish the wintering analysis and continue the investigations the next spring,” explains Professor Dr Bernd Grünewald, who leads the Bee Research Institute in Oberursel, Germany. Varroa destructor is a parasite that transmits viruses and diseases that can be deadly for honey bees. Colonies from both the treatment and the control fields were affected. “This study clearly shows the complexity of honey bee health, which is dependent on several factors. The study was designed to observe the influence of agriculture on bees but the real danger was a parasite,” says Dr Maus.

Beyond the scientific results, the study helped considerably to raise awareness of bee health for many participants: “During this study, I learned how critical and profoundly essential bee health is. Many other farmers became more aware of the subject as well,” says Thieß. Bayer plans to continue building the collaboration between beekeepers and farmers – bringing together the protection of plants with the welfare of bees.



Through this large-scale study conducted in winter rapeseed fields, it has been proven that growing this crop from seed treated with clothianidin is safe for all the tested bee species. Currently, Bayer is supporting additional testing for bee safety with neonicotinoids that is being carried out under realistic field conditions in Germany, Hungary and the United Kingdom. The company will continue to ensure that its agricultural crop protection products can be used safely near bees.


Honey Bee

Bee species with different lifestyles

The honey bee (Apis mellifera) is the most popular type of bee and has been domesticated. A honey bee colony during summer season typically consists of a single queen, several hundred drones and up to 60,000 female worker bees.

  • The Queen is predominantly responsible for reproduction. She will lay up to 2,000 eggs per day and lives for up to 4 years.

  • Worker bees which typically live for 4 to 6 weeks, keep the beehive going. They are, for instance, responsible for nursing the brood but they also collect nectar and pollen. The nectar is processed and stored by the bees as honey.

  • Drones are male bees which live for around 3 months. During summer, they mate with the young queens – mostly from other colonies. Afterwards, they will not be fed any longer and eventually are banished from the hive.
buff-tailed bumble bee

The buff-tailed bumble bee (Bombus terrestris) (Bombus terrestris) builds its colony during spring and summer – this is similar to honey bee colonies but there are less complex social structures. Nonetheless, the colony can comprise over 500 bumble bees and does adhere to a division of labor between the queens, the drones and the female workers. However, only one queen survives the winter and has to reproduce to build a new colony in spring.

Red Mason Bee

The red mason bee (Osmia bicornis) is a solitary bee species. It adapts well to its surroundings and uses hollow spaces for nesting, such as holes and insect tunnels in wood. Typically, the red mason bee’s nests are tubular with compartments made of clay. The red mason bee spends the winter in a natural cocoon.

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One of the world's largest field studies tests bee safety Rapeseed: A safe source of food?
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