Behavioral, regenerative, and reproductive responses of Girardia tigrina to imidacloprid exposure

This study evaluates the acute and chronic toxicity of imidacloprid (IMI), a neonicotinoid insecticide (NNI) commonly used worldwide, on the non-target planarian Girardia tigrina. The research is motivated by the frequent detection of IMI in aquatic ecosystems near agricultural areas, raising concerns about its adverse effects on non-target organisms. Acute toxicity was assessed by exposing planarians to IMI (Imidagold 700 WG®) at concentrations ranging from 50 mg a.i./L to 527 mg a.i./L, resulting in a 48-h LC₅₀ value of 94.29 mg a.i./L. Chronic toxicity (8-day exposure - locomotion and regeneration, 4 weeks - reproduction), was evaluated using IMI concentrations ranging from 100-1600 μg a.i./L. The results demonstrated a significant reduction in locomotion and a delay in the regeneration of photoreceptors and auricles at concentrations of 200 μg a.i./L. Cumulative reproduction (fecundity) was significantly impacted at concentrations of 100 μg a.i./L. In summary, this study highlights the significant impact of NNIs, specifically IMI, on the non-target planarian G. tigrina. Sublethal effects on behavior, regeneration, and reproduction of planarians highlight the potential risks that NNIs pose to freshwater invertebrates. The results suggest possible disruptions in planarian populations, emphasizing the need for multigenerational and population-level studies. Additionally, the observed effects emphasize the need for further research into detoxification mechanisms and adaptive responses in planarians to better understand the long-term consequences of continuous IMI exposure on population dynamics.