Insecticides containing flupyradifuron and sulfoxaflor can have devastating effects on honey bee health. The substances damage the insects’ gut flora, especially when combined with a common fungicide, making them more susceptible to disease and shortening their lifespan. This was recently shown by a study by the Martin Luther University Halle-Wittenberg (MLU) and the Helmholtz Center for Environmental Research (UFZ), which was published in science of the whole environment. The two insecticides were considered safe for bees and bumblebees when they were approved, but their use has since been severely restricted.
For the study, honey bees were first bred in the laboratory that were free from environmental influences. “We wanted to control every aspect of the bees’ lives – from their diet to their exposure to pathogens or pesticides,” says Dr. Yahya Al Naggar, the biologist who led the project at MLU and now works at Tanta University in Egypt. In the first few days, all the bees were given the same food: sugar syrup. They were then divided into several groups and various pesticides were added to their feed. One group received flupyradifuron, another sulfoxaflor. Both substances are approved as insecticides in Germany, but their use is now limited to greenhouses.
Since pesticides are often used in combination, the scientists also took this into account in their laboratory experiment by enriching the food of two other groups not only with the insecticides mentioned, but also with azoxystrobin, which has been protecting plants from harmful influences fungi for many decades. The concentration of the substances was well below the legal requirements. “Our approach was based on realistic concentrations that could be found in the pollen and nectar of plants treated with the pesticides,” says Al Naggar. A control group continued to receive the normal sugar syrup without additives.
Over a period of ten days, the team observed whether the substances had any effects on the bees and, if so, which ones. They found that the pesticides are anything but harmless: around half of all bees whose diet was supplemented with flupyradifuron died during the study – and even more when they were combined with azoxystrobin. While sulfoxaflor produced similar effects, more insects survived the diet.
The scientists also analyzed the bees’ intestinal flora, i.e. the bacteria and fungi that live in their digestive tract. “The fungicide azoxystrobin led to a significant reduction in naturally occurring fungi. That was to be expected since fungicides are used to control fungi,” says Dr. Tesfaye Wubet from the Helmholtz Center for Environmental Research (UFZ), which is also a member of the German Center for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig. However, over the course of the ten-day study, the team was able to show that the mixture of fungi and bacteria detected in the insects differed greatly from the control group, depending on the substances used. According to the researchers, the bacterium Serratia marcescens was able to spread alarmingly well in the digestive tract of the treated insects. “These bacteria are pathogenic and harmful to bees. They can make it harder for insects to fight off infection, which can lead to premature death,” explains Al Naggar.
Since the study was carried out in a laboratory in Halle to exclude the number of external influences, it is unclear whether the same results can be found in nature. “The effects of the pesticides could well be even more dramatic – or the bees could fully or at least partially compensate for the negative effects,” concludes Wubet. Against this background, the team calls for the potential effects of new pesticides on beneficial organisms to be researched more intensively before approval and for their effects on the intestinal flora to be included in the risk assessment as standard.
The study was funded by the Alexander von Humboldt Foundation with additional support from the EU-funded project Poshbee.
Materials provided by Martin-Luther-University Halle-Wittenberg. Note: Content can be edited for style and length.