Effects of Life Stage on the Sensitivity of Folsomia candida to Four Pesticides

The registration of pesticides in the European Union requires the assessment of the toxicity of active substances to soil invertebrates. The most commonly tested soil microarthropod species is Folsomia candida (Collembola), for which toxicity tests usually start with juveniles and determine survival and reproduction after 28 days of exposure, following Organisation for Economic Co-Operation and Development test guideline 232. Test duration may be shortened to 21 days by starting exposures with adult animals. The toxicity of chemicals can, however, vary significantly between different life stages (e.g., juveniles or adults) of the same species. In the present study, we assessed the toxicity of four active substances (cyproconazole, teflubenzuron, imidacloprid, and thiacloprid) to F. candida aged approximately 10 days (juveniles) and 20 days (adults) at the beginning of the tests. Tests were performed in LUFA 2.2 standard soil at 20 ± 2 °C, and effect concentration (ECx) values compared using likelihood ratio tests. The tests lasted 21 days for older springtails and 28 days for the younger ones. Life stage did affect the sensitivity of the springtails, with the survival and reproduction of younger animals being a factor of 2–6.5 more sensitive to the insecticides but not to the fungicide. For teflubenzuron and imidacloprid, the EC50 for younger springtails were 0.025 and 0.111 mg a.s. kg^–1 soil_dw, respectively, and for adults 0.048 and 0.264 mg a.s. kg^–1 soil_dw, respectively. For the younger animals the median lethal concentration values for teflubenzuron, imidacloprid, and thiacloprid were 0.353, 0.224, and 1.02 mg a.s. kg^–1 soil_dw, respectively, and 0.571, 0.446, and 6.91 mg a.s. kg^–1 soil_dw, respectively, for older animals. We discuss the implication of these differences for the risk assessment of pesticides to soil arthropods. Environ Toxicol Chem 2023;42:1782–1790.