The decline in bees is a sensitive issue, for which the agricultural sector is often blamed. However, diverse factors such as weather or the presence of parasites, which also influence the well-being of plant pollinators, are frequently overlooked. In fact, the agricultural sector has a growing number of tools at its disposal to do its part for the survival of its important little helpers. Across Europe projects are under way to face this very specific challenge.
In the field of crop protection, the direct, delayed, and combined effects of agriculture continue to be controversial, both in public and in academia. As long as technologies like RNA interference pesticides or the use of robots for weed control are still dreams of the future, there are opportunities to align cultivation measures during the flowering period with bees’ activity rhythms.
The foraging activity of bees depends on many factors including time of day/year, humidity, wind, or crop. Research is ongoing to better understand how these parameters interact. At the same time, technologies are also being developed to better understand and document the risks, such as connected beehives.
Validating good practices
In France, Vincent Henne has implemented three such systems on his farm. “Monitoring bees is a means of ensuring good practices,” says the young farmer in Heudicourt, who grows wheat, sugar beet, flax, barley, oilseed rape and legumes on his 135-ha farm. The beehives are equipped with scales, directly connected to the farm’s computer, for studying bee colony dynamics.
The bees are located on the edge of a one-hectare strip of fallow land, between two rapeseed plots. The rainy year of 2021 did not seem favourable for their activity. “Nevertheless, the average weight of our beehives increased to 35kg. With the help of software which plots the weight measurement dynamics on a curve, we were able to verify that the bees were feeding correctly throughout the season.”
By the end of May pollen beetle had infested the crop and pesticide was applied in the early evening. By checking pest traps installed on the plots, and the weight of the hives, Mr Henne was reassured there had been no decline in his bee populations. “I verified that my practices had no harmful effect on the bees’ activity.”
Monitoring bees – above all else – is a means of ensuring good practices.
Renewing the links
A similar project was initiated in Île de France in 2019. “Our goal is to renew links between society and agriculture by explaining the real interactions between agriculture and beekeeping, while promoting local honey production,” explains Elisa Despiney of the Departmental Federation of Farmers’ Unions (FDSEA). Twenty computer-connected weigh-scales were installed, and this network of farmers and beekeepers continues to expand, recording honey flow data.
“We realised that major food sources for pollinating insects are rapeseed and sunflower,” explains Nicolas Cerrutti, head of Functional Biodiversity Studies at the Terres Inovia Institute, which supplied the computer-connected scales to Mr Henne. “In some arable regions, bees depend mainly on rapeseed at the start of the season.” Comparisons were made between areas differing in the proportion of rapeseed grown. “We noticed in 2021 that the weight of the hives in areas with a higher share of rapeseed was significantly higher.”
The major food sources for pollinating insects are rapeseed and sunflower
Numerous factors determine bee health, including the weather and presence of parasites like the varroa mite or wax moth. The availability and diversity of flowering plants is one of the most important factors which can be heavily influenced by agricultural practice. Well-nourished bees are more stress resistant.
Connected beehives allow Vincent Henne to monitor the bees' activities on his computer, via the “optibee” software.
A beekeeper helps Vincent Henne to better understand bee health and to adapt his farming practices.
When agricultural crops do not provide sufficient food for pollinators, sowing melliferous (nectar producing) flowers close to arable fields can compensate for such deficits.In recent years, such initiatives have become increasingly popular. In Sweden, the Rural Economy and Agriculture Society (SREAS) has developed a programme to set up fallow land and flower areas, which has involved some 700 farmers. “This initiative comes from the agro sector itself, and not an obligation imposed by the regulatory authorities, which is the project’s strong point,” says Mattias Hammarstedt, agronomist and adviser to the regional office of SREAS, farming 145ha himself.
“We sow seed mixtures designed to attract pollinators.” This programme provides farmers with two free or reduced-price seed mixtures. One is annual (purple tansy, buckwheat, Persian clover, purple clover, sunflower). The other is perennial lasting for six years (purple tansy, buckwheat, Persian clover, red clover, white clover, caraway, and common trefoil).
»Farmers can help solve many environmental challenges. We want to make the public under-stand that we really care.«
These are designed to attract different types of pollinators, including bumblebees, honeybees, flies, butterflies, etc, as well as to provide as the longest possible flowering period. “According to some studies, the declining bumblebee population is the most acute problem in Sweden,” says Mr Hammarstedt. “We need to consider the different species of bumblebees, with short or long tongues, which need different types of flowers to be able to access the nectar.”
A better picture
The initial idea was to create an uninterrupted ecological corridor, a strategy which was subsequently revised. The sown area stretches over 800km. “Research has shown that it is best to spread out the areas in strips, but also as areas with perennial fields that provide food and habitat. This is because bumblebees fly only a few hundred metres from their hives,” he adds.
While most of the participants join this programme for ecological reasons, the farmers that grow rapeseed benefit most. Some participants also have orchards. “Most of the farmers tell us this approach is more rewarding than just leaving land fallow.”
Another benefit is the positive response from the public and media. “Besides the main objective of increasing biodiversity and generating food resources for pollinators, this helps people understand that farmers are not the problem, but rather that we can contribute to the solution of many environmental challenges. And that we really care.”
Sorghum in mixed cropping
The other avenue is to increase the floral diversity in fields. This can be done with more diverse rotations or cover crops. For example, an area of phacelia that covers only 0.1% of the foraging area can provide up to 90% of a beehive’s pollen harvest during a given period.
Plant breeding is another opportunity. In the case of sunflowers, for example, there is a hypothesis that selecting genotypes which are more resistant to water stress has led to a decline in nectar potential. So, it should be possible to select varieties to sow close to beehives based on the criteria of melliferous potential.
In Germany, the project SoBinEn – with multiple research partners – aims to enrich the floral supply on fields designated for growing energy crops. Launched in April 2020 this involves mixing crops to improve the quality and quantity of pollinators’ food supply.
The first results show that in mixed cultivation with suitable companion plants, a biomass yield just as high as monoculture sorghum can be achieved.
Sorghum millet (Sorghum bicolor L.) is grown as the main crop. Modern, medium-high dual-type varieties with a pronounced panicle are used, from which biogas can be easily produced. Since they provide plenty of pollen, they are also valuable for the bees. But the question of nectar supply remains. “We have set up test plots combining sorghum with various companion plants,” explains Dr Steffen Windpassinger from Justus Liebig University. “In one model sorghum and the associated crops are sown and harvested together. In the other, undersown crops are used, remaining in the field and continuing to grow after the sorghum harvest. The first results show that in mixed cultivation with suitable companion plants, a biomass yield just as high as monoculture sorghum can be achieved. We have yet to determine what the methane recovery looks like, but it can be assumed that a similar trend will be observed.”
Foraging increases methane potential?
At the right temperature and with sufficient water, sorghum is mostly self-pollinating and does not need insects for full grain growth. However, the researchers suspect that bees foraging for pollen in sorghum can help stabilise yields in stress situations and positively influence the crop’s methane-forming potential. According to this hypothesis, the colorful undercrops grown intermixed with sorghum attract bees to the sorghum field. During the project, researchers will analyse whether the attraction effect leads to the sorghum blossoms being visited more intensively and whether this improves the grain formation.
In collaboration with several seed companies, Dr Windpassinger, a specialist in sorghum breeding, is also studying the phenotypic characteristics of plants used for mixed cropping. “The objective is to ensure sufficient light and water resources for the nectar-bearing plants growing underneath the sorghum. This is why we evaluate sorghum plants using the criteria of vertical leaf arrangement, vertical rooting, and low tendency towards tillering. We are also seeking to define the optimum seeding density.”
Dr Rheinhold Siede of the Kirchhain Bee Institute is studying the effectiveness of the system in meeting bees’ dietary needs. “We cannot reveal definitive figures, but the nectar-bearing potential of some associated plantings has already been clearly confirmed.” By means of pollen analyses, the scientist determines which plants have been visited, and therefore which mixtures are the most attractive.
In Germany about 8% of agricultural land is dedicated to growing crops for energy production. “This is not about replacing biogas maize but rather supplementing it,” says Dr Siede. “However, it is obvious that mixing energy crops like sorghum with plants providing nectar creates opportunities for pollinators, but only if put into practice on a sufficiently large scale, and not simply as niche systems. The goal is to widen crop rotations, with or without under-sowing. Biodiversity will benefit from this, and therefore the bees.”