A three-year large scale study on the risk of honey bee colony exposure to blooming sunflowers grown from seeds treated with thiamethoxam and clothianidin neonicotinoids

Despite the restriction of use neonicotinoids in EU, including thiamethoxam and clothianidin, debate over their risk on honey bees has not been fully settled. This study presents results a three-year working with 180 bee colonies ten replicates. Colonies were sorted into three treatments (60 per treatment) exposed to sunflower blooms grown from seeds treated thiamethoxam, clothianidin non-treated control. Each colony was assessed at six moments: one before exposition sunflower, two during (short-time risk), after (medium-time risk) wintering (long-time risk). The health development by monitoring adult population, brood development, status queen, food reserves survival. No significant difference among when raw data considered. However, evolution initial evaluated, observed first week exposure blooms. In this period, number amount slightly lower hives neonicotinoids, although such differences disappeared subsequent evaluations. concentration residues samples beebread level ng·g-1. Magnitude effect treatment factor variability related parameters low. most important hive, followed replicate year, lesser extent strength colonies.