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 OECD 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 this 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 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 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 LC50 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.