Registration of veterinary medical products includes the provision that field tests may be required to assess potential nontarget effects associated with the excretion of product residues in dung of treated livestock (phase II, tier B testing). However, regulatory agencies provide no guidance on the format of these tests. In the present study, the authors report on the development of a standardized field test method designed to serve as a tier B test. Dung was collected from cattle before and up to 2 mo after treatment with a topical application of a test compound (ivermectin). Pats formed of dung from the different treatments were placed concurrently in the field to be colonized by insects. The abundance, richness, and diversity of insects developing from egg to adult in these pats were compared across treatments using analysis of variance tests. Regression analyses were used to regress abundance, richness, and diversity against residue concentrations in each treatment. Results of the regression were used to estimate mean lethal concentration (LC50) values. The robustness of the method and the repeatability of its findings were assessed concurrently in 4 countries (Canada, France, Switzerland, and The Netherlands) in climatically diverse ecoregions. Results were generally consistent across countries, and support the method's formal adoption by the European Union to assess the effects of veterinary medical product residues on the composition and diversity of insects in dung of treated livestock. Environ Toxicol Chem 2016;35:1934-1946. © 2015 Crown in the right of Canada. Published by Wiley Periodicals Inc., on behalf of SETAC.

Regular mowing of grassland is often necessary for plant conservation, but uncut vegetation is needed by many arthropods for overwintering. This may lead to conXicting management strategies for plant and arthropod conservation. Rotational fallows are a possible solution. They provide a spatio-temporal mosaic of mown and unmown areas that may combine beneWts to both plants and arthropods. We tested if rotational fallows enhance spider overwintering in fen meadows. Rotational fallows consisted of three adjoining strips 10 m wide and 35-50 m long. Each year, one of these strips was left unmown (fallow) in an alternating manner so that each strip was mown two out of three years. Spiders were sampled during spring with emergence traps in nine pairs of currently unmown fallow strips and completely mown reference plots. Fallows signiWcantly enhanced orb-weavers (Araneidae), sac spiders (Clubionidae) and ground spiders (Gnaphosidae). However, only 4.7% of the total variation in community composition was attributable to fallows. Community variation was larger between landscapes (34.5%) and sites (38.2%). Also diversity was much higher between landscapes (45 species) and sites (22 species) than between fallows and mown reference plots (10 species). We conclude that the Wrst priority for spider conservation is to preserve as many fen meadows in diVerent landscapes as possible. Locally, rotational fallows enhance overwintering of the above-mentioned spider families, which are sensitive to mowing in other grassland types as well. Thus, rotational fallows would probably foster spider conservation in a wide range of situations. However, stronger eVects can be expected from larger and/or older fallow areas.