Results of an international ring test with the dung fly Musca autumnalis in support of a new OECD test guideline.

A standardized bioassay using the face fly, Musca autumnalis L. (Diptera: Muscidae), was developed to test the lethal and sublethal toxicity of parasiticide residues in livestock dung. The repeatability of this test was assessed for the parasiticide 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. The calculated effect concentration at which 50% emergence was observed (EC50) averaged 4.65+/-2.17 (Standard Deviation (SD) microg ivermectin/kg fresh dung (range: 1.20-7.7)). Effects on emergence were, with one exception, not observed below the No Observed Effect Concentration (NOEC) ranging between 1.11 and 3.33microg ivermectin/kg. No effect on development time was observed. We conclude that the face fly is 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, this species was accepted as a possible test organism in a recently published OECD Guideline (No. 228).