Sub‐lethal effects of imidacloprid on bumblebees,Bombus terrestris (Hymenoptera: Apidae), during a laboratory feeding test

A laboratory feeding test was conducted on queenless micro‐colonies of three bumblebee workers (Bombus terrestris L) to study the effects of low doses of imidacloprid on pollen and syrup consumption, worker survival, brood size and larval development. Two doses were used: D1 = 10 µg AI kg⁻¹ in syrup and 6 µg AI kg⁻¹ in pollen; D2 was 2.5 times higher in syrup and 2.7 higher in pollen. During 85 days 27, 30 and 29 micro‐colonies were reared for control, D1 and D2 treatments respectively. Food consumption was not affected by either dose. During the 5‐day pre‐oviposition period the mean insecticide intake was 4.8 ng per day per worker in treatment D2. Both doses slightly but significantly affected worker survival rate by 10% during the first month, without any dose‐effect relationship. Brood production was significantly reduced in D1 treatment and larval ejection by workers was significantly lower in D1 and D2 than in control. No significant effect of D1 and D2 treatments on the duration of larval development was revealed. No residue could be detected in workers still alive after 85 days. It was concluded that the survival rate and reproductive capacity of B terrestris was not likely to be affected by prolonged ingestion of nectar produced by sunflower after seed‐dressing treatment with imidacloprid (Gaucho), since honey or pollen collected by honeybees foraging treated sunflower never revealed concentrations of imidacloprid higher than 10 µg kg⁻¹. © 2000 Society of Chemical Industry