New insecticides are bad news for bee health and their guts – ScienceDaily

Insecticides containing flupiradifurone and sulfoxaflor can have devastating effects on the health of honey bees. The substances damage the intestinal 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 Martin Luther University Halle-Wittenberg (MLU) and the Helmholtz Center for Environmental Research (UFZ), as published in Total environmental science. The two insecticides were considered harmless to bees and bumblebees when approved, but their use has since been severely restricted.

For the study, honey bees that were free of environmental influences were first reared in the laboratory. “We wanted to control every aspect of 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 early days, all the bees received the same food: sugar syrup. They were then divided into different groups and various pesticides were added to their food. One group was given flupiradifurone, while another was given sulfoxaflor. Both substances are approved insecticides in Germany, but their use is now limited to greenhouses.

Since pesticides are often used as a mixture, the scientists also took them into account in their laboratory experiment, enriching the food given to two other groups not only with the mentioned insecticides, but also with azoxystrobin, which was used to protect the plants. from harmful agents. mushrooms for many decades. The concentration of the substances was in any case well below the legal requirements. “Our approach was based on the realistic concentrations that could be found in the pollen and nectar of plants that have been treated with the pesticides,” says Al Naggar. A control group continued to receive regular sugar syrup without additives.

Over a ten-day period, the team looked at whether the substances had effects on bees and, if so, which ones. They found that pesticides are far from harmless: About half of all bees whose diets had been supplemented with flupiradifurone died during the study, and even more when combined with azoxystrobin. While sulfoxaflor produced similar effects, more insects survived the diet.

The scientists also analyzed the gut flora of bees – the bacteria and fungi that live in their digestive tract. “The azoxystrobin fungicide led to a significant reduction in naturally occurring fungi. That was to be expected, as fungicides are used to control fungi,” says Dr Tesfaye Wubet of the Helmholtz Center for Environmental Research (UFZ) , which is also a member of the German Center for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig. Over the course of the ten-day study, however, 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 Serratia marcescens bacterium was able to spread alarmingly in the digestive tract of treated insects. “These bacteria are pathogenic and harmful to bee health. They can make it harder for insects to fight infections, leading to premature death,” says Al Naggar.

As the study was conducted in a Halle laboratory to rule out the number of external influences, it is unclear whether the same results can be found in nature. “The effects of pesticides could be even more dramatic, or the bees could be able to fully or at least partially offset the negative effects,” concludes Wubet. With this in mind, the team calls for the potential effects of the 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 the risk assessment.

The study was funded by the Alexander von Humboldt Foundation with additional support through the EU-funded “Poshbee” project.

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