Swedish monitoring data reveal negative effect of neo-nicotinoids on bumblebee abundance

Abstract

Neo-nicotinioids are used as insecticides in a variety of crops, e.g. as seed-coating, but have also been found lethal to pollinating insects. In 2013, the European Union introduced a moratorium on some of these compounds. At the same time, the Swedish monitoring program NILS (National Inventory of Landscapes in Sweden) had completed its first round and today a second round has been completed. Thus, it is possible to analyze the effect of the moratorium on monitoring data on bumblebees in N=419 sites in southern Sweden. The presence of neo-nicotiniods was assessed using the official records of the type of crop grown on a field (Blockdatabasen), maintained by the Swedish board of Agriculture. The change in bumblebee abundance was compared to the area of different crops in the surrounding landscape. We tested the hypothesis that abundance of bumblebees increased more in landscapes with more oilseed rape (a common crop where seeds previously were coated with neo-nikotinoids). We found no effect on diversity but significant increase in abundance for some species (Bombus pascuorum, B. lucorum) while other did not change (B. terrestris). There was no effect of connectivity of oilseed rape fields in the surrounding landscape, and no evidence of a threshold: it was mostly enough with one field to see an increase after the moratorium. The fact that bumblebee populations recover indicate that the negative effect is mediated directly via the crop. Our study is a nice example of how monitoring data paired with official data can be used for large scale biodiversity studies.