Acute toxicity of the insecticide Imidacloprid and the herbicide 2,4-D in two species of tropical anurans

The use of pesticides has notably increased in recent years globally. However, sensitive organisms exposed to these environmental pollutants, such as amphibians, may experience adverse effects. The insecticide imidacloprid (IM) and the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) are two pesticides commonly used in Colombia, but their toxic impacts on tropical anurans remain poorly understood. In this study, we tested the acute toxic effects of IM and 2,4-D on the survival, total length, and burst swimming speed of tadpoles from two anuran species. Under laboratory conditions, the tadpoles of Boana platanera and Engystomops pustulosus were independently exposed to each pesticide for 96 h. We found that the tadpoles of E. pustulosus were more sensitive to both IM and 2,4-D than those of B. platanera. However, the LC₅₀ values were higher than the reported field concentrations for these pesticides. IM led to a reduction in the total length of B. platanera tadpoles and induced total immobility in surviving individuals of both species. In contrast, the herbicide 2,4-D did not affect the total length or the swimming speed of tadpoles from the two species. In conclusion, based on the results and the reported field concentrations, IM and 2,4-D are not lethal to the studied anurans. Nevertheless, it is important to consider that IM caused strong negative sublethal effects on tadpoles, which could compromise their survival in the future. Finally, we also found that the insecticide IM showed notably greater toxicity to the tested species than did the herbicide 2,4-D.