The effect of pesticide mixtures on bees

Scientists have assessed the risk of exposure to pesticide mixtures in different species of bees. As a result, they make various recommendations to support the health of pollinators and the overall well-being of the ecosystem.

The decline in bee populations globally poses a threat to the reproduction of wild plants and crops, which can have a negative impact on food production and the balance of ecosystems. The use of pesticides has been identified as one of the main causes of this decline. Bees can be exposed to them when they consume nectar and pollen from crop flowers and surrounding plants.

In a study carried out by researchers from the Polytechnic University of Madrid (UPM) in Spain and the University of Bologna (UNIBO) in Italy, pesticide residues in the pollen and nectar of flowers from melon fields in the Madrid Tagus Basin in order to assess the potential risk of exposure to mixtures of pesticides in different species of bees. In addition, the work has carried out a chronic oral toxicity test in bumblebee microcolonies using one of the most frequent mixtures of pesticides. The results obtained have significant implications for improving pesticide risk assessment schemes to ensure the conservation of pollinators.

Traditionally, ecotoxicology studies estimate pesticide exposure by analyzing pollen collected from honey bees for residues. However, the team led by Celeste Azpiazu, from the UPM, suggests that examining the residues directly on the flowers provides a more precise measure of exposure. “Residues found in pollen collected by honey bees are often mixed with nectar or other glandular secretions that can dilute their concentration. Nor will the measurements of residues of bees exposed to lethal or sub-lethal doses that do not return to the hive be present, ”says Celeste Azpiazu. Furthermore, she continues, “many studies focus on individual pesticides. However, in agricultural landscapes it is common for bees to encounter mixtures of products during their foraging.”

The research results revealed the presence of 19 pesticide active ingredients in the flowers of melon fields, including insecticides, fungicides and herbicides. Interestingly, 11 of these active ingredients had not been applied during the season in which the samples were taken, suggesting that they may have accumulated in the soil, contaminated irrigation water, or been dispersed from neighboring fields. These pesticides were detected mainly in pollen, while only four of them were found in the nectar and at lower concentrations.

Honey bee visiting a melon flower. (Photo: Celeste Azpiazu)

While current risk assessments only consider the honey bee, the authors of the new study looked at the risk of exposure to multiple pesticides in three species: the honey bee, the bumblebee, and the solitary bee, all of which are recommended for inclusion in the list. environmental risk assessments by the European Food Safety Authority (EFSA). Solitary bees were the most vulnerable, followed by honey bees and bumblebees. The insecticide imidacloprid was identified as the main contributor to the risk for these species. “It should be noted that the use of imidacloprid in the European Union has been restricted after the data for this study was collected. Now its application is limited to permanent greenhouses where the plants complete their entire life cycle”, comments Elisa Viñuela, also a researcher at the UPM and co-author of the study.

On the other hand, when tests were carried out with a mixture of insecticides commonly used in the study area in bumblebee microcolonies, no significant differences were observed in terms of mortality, pollen and syrup collection, or offspring production. This may be because the concentrations of the insecticides tested were low. However, the members of the work team suggest the need to carry out more studies in other bee species to obtain a more complete picture.

In summary, the results of this study highlight the importance of considering not only honey bees, but also other species in pesticide risk assessments. In addition, the importance of taking into account the sublethal and synergistic effects of these chemicals is highlighted. Therefore, carrying out these tests before placing new pesticides on the market is essential to guarantee the health of pollinators in agrosystems.

The study is titled “Pesticide residues in nectar and pollen of melon crops: Risk to pollinators and effects of a specific pesticide mixture on Bombus terrestris (Hymenoptera: Apidae) micro-colonies”. And it has been published in the academic journal Environmental Pollution. (Source: UPM)