How do they deal with food scarcity in late summer?

Late summer in Lower Franconia: There are almost no flowering plants left, and honeybee food is scarce. Researchers at the Biocenter investigated how bees cope with this situation.

Plants produce large quantities of nutrient-rich pollen in their flowers – a real powerhouse for many insects, including honeybees: they mix the protein- and fat-rich pollen into the food they use to feed their larvae. Younger bees also consume pollen themselves to build their strength.

These plant energy sources are extremely important to honeybees. A lack of pollen can delay their growth, making them more vulnerable to pathogens and more sensitive to pesticides. Scientific studies also show that a more diverse pollen mix improves the health and winter survival of bee colonies.

Potential double burden: food shortages and pesticides

So late summer must be a particularly difficult time for honey bees. At this time of year, few plants are thriving and food supplies are dwindling. In addition, pollen that is still available may contain residues of pesticides used in agriculture.

This double burden can be particularly difficult for bees, especially during a season that is already crucial to them: in late summer, long-lived winter bees develop in hives. Their vitality determines whether the colony will survive the cold season unscathed.

Beehives placed in the Lower Franconia region

So what is the nutritional status of honey bees in late summer, especially in agricultural areas? Researchers from the Chairs “Animal Ecology and Tropical Biology” and “Behavioral Physiology and Sociobiology” at the Biocenter of the University of Würzburg investigated this question. They placed 36 honey bee colonies in nine different locations in Lower Franconia. The proportion of annual agricultural land varies greatly around each beehive, ranging from 43 to 97% within a two-kilometre radius.

From the beginning of July to mid-August, the researchers took samples from pollen traps in front of the beehives every three days. They analyzed the plant species visited by the bees and studied pollen diversity and pesticide residues. Results Posted in Agriculture, ecosystems and environment.

Same pollen diversity and lower levels of pesticides

The results surprised the team led by Professor Ingolf Stefan Dewinter and Ricarda Scheiner: the diversity of pollen collected was always similar, regardless of whether there was a large or small amount of annual farmland surrounding the beehives. What is also unexpected is that the pollen contains only small amounts of pesticides.

Could honeybees also thrive in agricultural areas with intensive plantings in late summer?

Doctoral student Sarah Manzer, lead author of the publication, offers a caveat: “Our results should not be overgeneralized. In our study, landscapes with a high proportion of annual cropland still contain many different fields. These can provide flowering resources along field edges as well as a range of pollen-producing weeds within different crops.” In other countries with much larger areas of arable land, such as the United States, the landscape may provide much less food.

Furthermore, different countries have different regulations on the use of pesticides, which may lead to varying levels of pesticide contamination. In order to get a comprehensive picture of the impact of farmland on honeybees, it is necessary to conduct more studies in other areas and at other times of the year, especially in the spring, when more pesticides are used.

Alfalfa is at the top of pollen suppliers

“The DNA analysis revealed 140 different pollen types in our 540 pollen samples,” says doctoral student Manzer. Bees most often collect pollen from clover species, followed by cornflower pollen and sunflower pollen.

On average, bees carry pollen from 10 different plants to the hive over the course of three days. This is neither a large nor a small amount. Similar values ​​have been reported in other studies. Bees may compensate for the scarcity of flowers in late summer by flying greater distances in search of food.

About 60% of the samples are free of pesticides

The researchers found pesticide residues in 39% of the pollen samples. Of the 16 pesticides discovered, fungicides (agents used to control fungi that damage plants) were the most common.

“In terms of concentration, the doses of pesticides found range from moderate to low, and no direct lethal effects on honeybees can be expected,” says Manzer, based on the results of various scientific studies. However, “we cannot rule out the possibility of gradual harm to bees through long-term negative effects. Furthermore, there is limited knowledge about potential interactions with other insecticides. We also do not know the impact on much smaller wild bees, for example.” More studies are needed to shed more light on this issue.