Effects of two chordotonal-organ-targeting insecticides on survival and locomotion of Melipona beecheii and Nannotrigona perilampoides (Apidae: Meliponini)

Abstract

Chordotonal organs are vital for survival, allowing insects to navigate, communicate, and detect predators or prey effectively. However, little is known about the toxic effects of chordotonal-organ-targeting insecticides (COTI) on stingless bees. Here, we evaluated the toxicity of commercial formulations of two COTIs, flonicamid and pymetrozine, on stingless bees Melipona beecheii and Nannotrigona perilampoides. After acute oral and contact exposure to field-recommended concentrations (flonicamid: 250 mg a.i./L and pymetrozine: 500 mg a.i./L), survival rates, walking speed, and flight take-off activity were assessed. Overall, the toxic effects of the insecticides were more pronounced in M. beecheii and when bees ingested the insecticides. Survival rates dropped to 23–32% in M. beecheii and 77–94% in N. perilampoides when exposed to the insecticides. In M. beecheii, oral exposure to insecticides decreased walking speed to 0.14–0.95 cm/s, compared to 3.30–3.74 cm/s for the control group. For contact exposure, only pymetrozine caused a significant reduction in walking speed (0.48–1.21 cm/s) compared to the control group (1.85–2.61 cm/s). In N. perilampoides, both oral and contact exposure to insecticides reduced walking speed to 0.43–0.49 cm/s, compared to 1.07–1.18 cm/s for the control group. The insecticides also significantly reduced flight take-off activity, with only 6.7% of M. beecheii adults and none of the N. perilampoides adults being able to fly after oral or contact exposure, compared to 70 and 80% of the bees in their respective control groups. Our findings demonstrate the vulnerability of stingless bees to COTIs, highlighting the urgent need for stricter pesticide regulations to protect pollinator health.