Dietary Chlorantraniliprole Suppresses Reproduction in Worker Bumblebees

The study examined the effect of the insecticide chlorantraniliprole to Bombus terrestris (buff-tailed bumble bee) microcolonies.  Chlorantraniliprole is a systemic insecticide in increasingly use in agricultural and other settings. In target pests, this insecticide has been demonstrated to interfere with embryonic and larval development, as well as causing lethargy and feeding cessation.

The effects of chlorantraniliprole at a range of concentrations (0.4 – 40 mg/L  - corresponding to 0.1% - 100% of Maximum Field Recommended Concentration (MFRC)) was tested through three different exposure routes: topically, through ingestion of contaminated sugar water, or through ingestion of contaminated pollen, over a period of 7 weeks.

Consumption of sugar water treated with 20 and 40 mg L-1 of chlorantraniliprole resulted in 79% mortality within 72 hours in each case, while over the seven week period, these concentrations resulted in ≥95% mortality. At 4 mg/L of chlorantraniliprole in sugar water, no mortality occurred within 72 hours, and at 0.4 mg/ L no mortality occurred over the 7-week exposure period. Based on these results, the acute LC50 was calculated at 13 mg/L and the chronic LC50 at 7 mg/L. Oral exposure via pollen ingestion and via topical application resulted in < 25% mortality during the 7 week period.

However, pollen treatment did affect reproduction (production of drones). Compared to controls, significant decreases were seen at 0.4 mg/L with treated pollen, while exposure to sugar water resulted in significant differences at 4 mg/L.

Workers and drones exposed to 0.4 and 40 mg/L of chlorantraniliprole on pollen were lethargic in 88 and 50% of the microcolonies treated, respectively.