Impact of thiamethoxam on Folsomia candida and Hypoaspis aculeifer in artificial and natural soils.

Neonicotinoid insecticides are widely used in agriculture due to their effectiveness in controlling pests. However, their non-selective nature also affects non-target organisms, such as collembolans and mites, which play essential ecological roles and are highly sensitive to environmental changes. This study assessed the toxicity of thiamethoxam (TMX) on the survival and reproduction of the springtail Folsomia candida and the predatory mite Hypoaspis aculeifer in both an artificial (Tropical Artificial Soil - TAS) and a natural soil (Petric Plinthosol - FFc). Soils were spiked with the commercial insecticide CRUISER® 350 FS (35% thiamethoxam). Seven concentrations were tested for F. candida (0.13-1.42 mg/kg dry soil) and six concentrations for H. aculeifer (1-400 mg/kg dry soil), based on the organisms' sensitivities and recommended doses (RD) for use in sunflower crops (Syngenta, 2025). Thiamethoxam significantly affected both species. Folsomia candida demonstrated greater sensitivity than H. aculeifer. In both cases, toxicity was more pronounced in FFc. A 50% reduction in F. candida reproduction occurred at 0.8 mg TMX/kg dry soil in FFc, whereas in TAS, the same reduction was observed only at 1.6 mg TMX/kg dry soil. Besides, the concentration affecting springtails in FFc was three times lower than the mentioned RD. These findings underscore the influence of soil types on insecticide toxicity and highlight the importance of assessing pesticides impacts in different soils. Furthermore, testing multiple soil organisms enhances the ecological relevance of toxicity studies, contributing to understanding pesticide impacts on soil communities.