Wild bees depend on the landscape structure

Organic farming and flower strips are financially supported by the European Union in order to enhance populations of wild bees and hoverflies, which are major pollinators of most crops and wild plants. The research team selected nine landscapes in the vicinity of Göttingen along a gradient of increasing field size and then analysed the wild bees and hoverflies in each landscape at the edge of an organic wheat field, in a flower strip along conventional wheat, and at the edge of a conventional wheat field without flower strips. The result: most pollinators were found in the flower strips, but organic fields, characterized by more flowering wild plants than conventional fields, were also beneficial. Bumblebee colonies established on the margins of fields as part of the project produced more queens in flower strips when located in landscapes with small conventional fields. In contrast, large areas were particularly advantageous when it came to flower-rich organic fields. Flower strips offer a high local density of pollen and nectar, but organic areas compensate for this by their increased area.

"The results show that action at both local and landscape level is important to promote wild bees," emphasises Costanza Geppert, first author of the study. The investigations were part of her Master's thesis in the Agroecology Group in the Department of Crop Sciences at the University of Göttingen. "Wild bees and other insects cannot survive in a field simply by making improvements to that field, they depend on the structure of the surrounding landscape," adds Head of Department Professor Teja Tscharntke. "Therefore, future agri-environmental schemes should take more account of the overall landscape structure," adds Dr Péter Batáry who initiated the study.