Insecticides containing flupyradifuron and sulfoxaflor can have devastating effects on bee health. The substances damage the gut flora of insects, especially when used in conjunction with a common fungicide, making them more susceptible to disease and shortening their lifespan. This was recently demonstrated in a study conducted at the Martin Luther University Halle-Wittenberg (MLU) and the Helmholtz Center for Environmental Research (UFZ), as published in Science of the Whole Environment. The two insecticides were considered harmless to bees and bumblebees when they were approved, but their use has since been severely restricted.
For the purposes of the study, honey bees, which are not exposed to environmental influences, were first reared in the laboratory. “We wanted to control every aspect of the bees’ lives, from their diet to their exposure to pathogens or pesticides,” says Dr. Yahya Al Nagar, the biologist who led the project at MLU and who now works at Tanta University in Egypt. For the first few days, all the bees received the same food: sugar syrup. They were then divided into several groups and various pesticides were added to their food. One group was given flupyradifuron while another was given sulfoxaflor. Both substances are approved insecticides in Germany, but their use is now restricted to greenhouses.
Since pesticides are often used as a mixture, the scientists also took this into account in their laboratory experiment by enriching the food given to two other groups not only with the mentioned insecticides, but also with azoxystrobin, which is used to protect plants from harmful fungi in for many decades. The concentration of the substances is well below the legal requirements in any case. “Our approach was based on the realistic concentrations that can be found in pollen and nectar from plants that have been treated with the pesticides,” says Al Nagar. A control group continued to receive normal sugar syrup without additives.
For ten days, the team observed whether the substances had any effect on the bees, and if so, what. They found that the pesticides were anything but harmless: About half of all bees whose diets were supplemented with flupyradifuron died during the study—and even more when combined with azoxystrobin. While sulfoxaflor produced similar effects, more insects survived the diet.
Scientists have also analyzed the intestinal flora of bees, i.e. the bacteria and fungi living in their digestive tract. “The fungicide Azoxystrobin resulted in significant reductions in naturally occurring fungi. This was to be expected, as fungicides are used to control fungi,” says Dr. Tesfaye Wubet of the Helmholtz Center for Environmental Research (UFZ), who 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 found in the insects differed significantly 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 bee health. They can make it difficult for the insects to fight the infection, leading to premature death,” explains Al Nagar.
Since the research was conducted in a laboratory in Halle to rule out a number of external influences, it is not clear whether the same results can be found in nature. “The effects of pesticides may be even more dramatic – or bees may be able to completely or at least partially compensate for the negative effects,” concludes Ubett. With this in mind, the team calls for the potential effects of new pesticides on beneficial insects to be studied more rigorously before they are approved, and for their effects on aspects such as gut flora to be included as a standard in risk assessment.
The study was funded by the Alexander von Humboldt Foundation with additional support through the EU-funded Poshbee project.
Materials provided by Martin-Luther-University Halle-Wittenberg. Note: Content may be edited for style and length.