Adverse Effects of the Neonicotinoid Thiacloprid Assessed on an Ant Used as a Biological Model *

Abstract

Thiacloprid has been banned in many European countries for its toxicity, but is nevertheless still used outside the EU. Using the ant Myrmica sabuleti as a model organism, we sought a concentration of thiacloprid that would be low in environmental impact, but nonetheless harmful to an insect. Assessed on ten biological traits, a sub-lethal 2 μg/L concentration in the sugar water diet of the ants impacted their locomotion and other motor-linked behavioral traits such as orientation, moving on an unfamiliar device, moving on a rough surface, brood caring and progressing along a twist and turns path. Sensory perception appeared unaffected. Behaviors involving cognition or related in some way to it, such as social relationships, ability to leave an enclosure, learning and memory also appeared unaffected, but their outcomes could be entangled with those of locomotor impairment. The effect of thiacloprid on locomotion vanished in about 30 hours. Adverse effects were still present with the 0.1 and 0.01 μg/L concentrations, but at a lower level. Partial physiological adaptation at the individual level occurred for the 2 μg/L concentration, less so for 0.1 μg/L and not for 0.01 μg/L. Thiacloprid should thus be used at the lowest still active concentration producing a significant damaging behavioral effect with no physiological adaptation. This concentration remains to be specifically defined for targeted pest species.