Lack of Effects On Bumblebee (Bombus Terrestris) Colony Development And Drone And Queen Production Due To The Insecticide Chlorantraniliprole

The aim of the study was to investigate the potential impact of the insecticide chlorantraniliprole on queen-right bumblebee (Bombus terrestris) colonies under semi-field conditions in Phacelia tanacetifolia. The P. tanacetifolia crop was grown in soil treated with modelled worst-case 20-year plateau concentration of chlorantraniliprole in the top 20 cm of soil (equivalent to 0.088 mg a.s./kg). Additionally, two chlorantraniliprole spray applications at 60 g a.s./ha were made. In treatment T1 both spray applications took place before P. tanacetifolia flowering at growth stages BBCH 51–55 and BBCH 55–59. In T2 one spray application was conducted before P. tanacetifolia flowering at BBCH 55–59 and one application during P. tanacetifolia flowering and during daily bee flight at BBCH 61–62. The application in the control (C) and reference item treatment (R) (400 g dimethoate a.s./ha) was carried out during full P. tanacetifolia flowering and bumblebee flight. The bumblebee colonies were exposed to the treated flowering P. tanacetifolia crop for 20 days in the tunnels and afterwards the colonies were kept on a monitoring site. Results of this study indicate no significant differences between the chlorantraniliprole groups T1 and T2 and the control regarding all parameters assessed (i.e. adult and larval mortality, flight activity at the hive entrance, colony weight development, condition of the colonies and production of young queens and males). Overall, no effects of chlorantraniliprole on B. terrestris colonies including queen/male production, adult and larval survival, colony development and forager flight activity were found in this worst-case exposure set-up.