Determination of developmental toxicity of a test chemical to dipterian dung flies
The aim of the project was to standardise a test guideline with two dung fly species to be used for the environmental risk assessment of veterinary pharmaceuticals, in particular endo- and ectoparasiticides excreted in dung. The test is designed to evaluate developmental toxicity of a test substance to the dung dwelling life stages of dung-dependent dipteran species. The yellow dung fly, Scathophaga stercoraria (Scathophagidae), and the face fly, Musca autumnalis (Muscidae), are suitable indicator species, since they are widespread in Europe, Asia, Africa and North America. Both species are dung-dependent and multi-voltine, do not undergo obligate diapause, are easy to culture and have a short life-cycle that makes it possible to determine effects on development and survival in the laboratory. Due to the ecological role of these test species (a predatory and a saprophagous fly from different families), test results are relevant for the protection of dung fauna and their function. The proposed guideline has been developed by the Dung Organism Toxicity Testing Standardisation (DOTTS) Group, a SETAC advisory group. Practicability, sensitivity and robustness of the guideline were investigated in a ring test with seven laboratories from Germany, the United Kingdom, Switzerland, and Canada. In the case of the yellow dung fly (S. stercoraria), the lethal and sublethal toxicity of the parasiticide ivermectin was assessed in thirteen tests, showing an acceptable range of heterogeneity. An additional oviposition choice test revealed that yellow dung fly females do not discriminate among dung containing different ivermectin concentrations. In the case of the face fly (M. autumnalis), test repeatability was assessed for ivermectin in seven tests performed in four laboratories in Germany and France. Additional results of limit tests were provided by two laboratories from the UK. Test results had an acceptable range of heterogeneity. It is concluded that both the yellow dung fly and the face fly are suitably sensitive, and the methods sufficiently repeatable to support use of this standardized bioassay by the international community in the registration of new veterinary pharmaceuticals. Following these considerations, both species were accepted as test organisms in the OECD Guideline No. 228.