Abstract In recent years, the interest has increased for testing nonstandard species in the environmental risk assessment of pesticides. Especially mayflies seem to be of interest, because of their relevance in aquatic ecosystems, their potential sensitivity, and their vulnerability. So far there is a lack of standardized methodologies in acute and chronic testing of mayfly species. While acute testing of field-collected nonstandard species represents few challenges, especially chronic testing needs better and more detailed evaluation regarding the robustness and suitability of testing methods. Therefore, we conducted an inter-laboratory comparison of chronic experimental designs for the mayfly Cloeon dipterum. These methods were established in the two participating laboratories and were tested using a cross-design experiment. The test designs differed mainly in the feeding and light conditions. In addition, the influence of species origin was investigated and the Cloeon Development Index (CDI) was established to allow for a standardized evaluation of mayfly development. Our study showed that experimental design, especially the method of feeding, had a huge impact on larval development, while the origin of the organisms played a minor role. However, it was demonstrated that the mortality rate was higher for larvae that were transported between the participating laboratories than for larvae collected near each testing site. The presented work is not meant to be input for an Organisation for Economic Co-operation and Development test guideline but tries to provide necessary basic information for the performance of robust chronic studies with the mayfly C. dipterum. Based on these results, recommendations can be provided for an experimental design of a chronic test and on validity criteria regarding control survival and development rates for chronic testing of C. dipterum.
Classen et al. (Tue,) studied this question.