Dietary chlorantraniliprole suppresses reproduction in worker bumblebees

Pollinators such as the bumblebee, Bombus terrestris, fulfil a crucial role in agriculture. In this context, tests were conducted with the insecticide chlorantraniliprole (Coragen®) as a model compound active on the ryanodine receptor of insects.

Chronic oral exposure via pollen induced lethargic behaviour in B. terrestris workers and their offspring (drones). Indeed, in nests exposed to 0.4 mg L(-1) , representing 1/100 of the concentration recommended for use in the field, workers and drones did not take their defensive position upon stimulation and they were less active than non-exposed insects. The different risk assessment tests used here demonstrated that contact and pollen exposure had no effect on bumblebee worker survival, whereas oral exposure via sugar water caused both acute (72 h LC50  = 13 mg L(-1) ) and chronic (7 week LC50  = 7 mg L(-1) ) toxicity. Severe sublethal effects on reproduction were recorded in nests orally exposed to pollen treated with chlorantraniliprole.

The present study identified an important physiological endpoint of sublethal effects on reproduction, as this is associated with lethargic behaviour after oral intake. As such, this is a factor that should now be incorporated into future risk assessments. Secondly, it confirmed that the assessment of sublethal effects on behaviour is needed for adequate risk assessment of 'potentially deleterious' compounds with a neurogenic target, as is also pointed out in the recent European Food Safety Authority (EFSA) guidelines.