Enhancing wild bees in agricultural landscapes
Abstract: The movement of insects in agricultural landscapes has been a major research topic ofthe Applied Entomology group at ETH Zurich for two decades. This paper provides a synopsis ofthe key findings from our recent field experiments with wild (solitary) pollen specialist bees onfarmland. To provide their brood cells with pollen and nectar, these bees have to commutebetween their nesting site and the flowering host plant, but critical distances as well as thepotential impact of landscape barriers were largely unknown yet. To understand the effect oflandscape barriers on foraging activities, we released marked bees from the nest to forage acrosslandscape structures. Our findings indicate that landscape structures such as forests or rivers arenot insurmountable barriers for the bee species tested. To evaluate the effect of small vs. largedistances between the crucial resources on wild bees and their reproduction, we used a newexperimental approach in which patches of host plants were moved progressively further awayfrom the nest over time. Results document conclusively that solitary bees can travel unexpectedlylong distances between nest and flower resources. However, only few individuals of a speciesforage over long distances, whereas most individuals cover only few hundred metres.Furthermore, long foraging flights come at the cost of substantially fewer offspring. Hence aclose neighbourhood of foraging habitats and nesting sites within few hundred metres areimperative to ensure the persistence of these pollinator populations. Switzerland reimbursesfarmers that leave a small proportion of their land uncropped or covered with sown floweringplants, and we conclude that the spatial arrangement of these areas will provide importantopportunities for maintaining pollinator diversity.