Honey bee dance decoding and pollen-load analysis show limited foraging on spring-flowering oilseed rape, a potential source of neonicotinoid contamination

Abstract

Neonicotinoid insecticides used to treat the seeds of bee-attractive crops occur in trace amounts in nectar and pollen. Possible harm to bees has resulted in the European Commission imposing a precautionary two-year moratorium on the use of neonicotinoids on bee-attractive crops from 2013. Recent laboratory and semi-field studies on colony-level effects of neonicotinoids assumed exclusive or near-exclusive levels of colony foraging on a treated crop. But is this a realistic assumption? Six honey bee (Apis mellifera) colonies were monitored over two springs (April–May 2011/12) in two neighbouring locations (urban and rural) in and near Brighton, UK, to quantify foraging on oilseed rape, the most widespread bee-attractive crop in the UK, by decoding waggle dances and trapping pollen. The study area was representative of the UK agricultural landscape in that the percentage area cover of the blooming oilseed rape fields around the rural location was similar to the national average (3.3–3.9% vs 3.1%). The amount of foraging on oilseed rape fields, as indicated by dance decoding, was variable, but low, 0–0.02% for the urban and 2–26% for the rural location. Almost all foraging, 91–99%, was within 2km, even though honey bees can forage at distances of over 10km. Pollen trapping in 2012 supported the dance decoding results, with oilseed rape pollen comprising 14% of pollen pellets collected by foragers from rural and 4% from urban hives. The results of this study have implications for policy as they cast doubt on the generality of some previous studies on colony-level effects on social bees conducted in laboratory and semi-field settings.