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RESEARCH PRODUCT

Effects of soil organic matter content and temperature on toxicity of dimethoate toFolsomia fimetaria(Collembola: Isotomiidae)

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The purpose of these experiments was to study the effects of two major environmental factors, soil organic matter content (1.4–8.6%) and temperature (10–20°C), on chemical toxicity to a soil-dwelling collembolan Folsomia fimetaria. Dimethoate was used as a reference chemical. Effects on survival, reproduction, and juvenile size were investigated. Increasing soil organic matter content reduced toxicity significantly, but the differences disappeared when results were recalculated and expressed as soil pore-water concentrations. This supported the soil pore-water hypothesis. The effects of soil temperature were not so clear, because temperature affects not only the growth and reproduction of the collembolan but also the chemical degradation. In general, decreasing temperature seemed to increase toxic effects. The procedure for toxicity testing with F. fimetaria was further improved by using adults at stage 7 to 8, when males and females could reliably be distinguished by size. Furthermore, image processing was applied for the first time in the counting and size measurements of the collembolans.