Protocol for assessing the impacts of the insecticide Mospilan SG (acetamiprid) and the fungicide Folicur (tebuconazole) and their combination on the solitary bees Osmia bicornis and O. brevicornis under semi-field conditions

Pesticide effect studies on pollinators focus predominantly on the Western honeybee, Apis mellifera , which is also the only species for which EU regulations require risk assessment. Reliance on A. mellifera as the only model species for pollinators has been widely criticized, as its life history traits may lead to differences in pesticide sensitivity and exposure compared to other species. Therefore, current guidelines by EFSA recommend testing also on bumblebees and solitary bees, which has been done in practice almost exclusively on the generalist species Bombus terrestris and Osmia bicornis . Oligolectic bee species remain largely overlooked, which is concerning as they have experienced greater range reductions than generalist species. In addition, pesticide risk to pollinators is typically assessed for individual compounds or products, even though in reality pollinators are exposed to a mixture of several pesticides where synergistic effects may occur. Here, we present a protocol for a semi-field experiment that assesses the effects of two pesticides and their combination on the oligolectic Osmia brevicornis and the generalist O. bicornis . Conducted as part of the EU project WildPosh, the experiment builds on laboratory studies investigating pesticide impacts on pollinator health and is designed to test the effects of realistic exposure levels. Specifically, the experiment, for which we detail the methodology here, tests the insecticide Mospilan SG (a.i. acetamiprid), the fungicide Folicur (a.i. tebuconazole), and their combination. The study follows a full-factorial design using 40 flight cages across four spray treatments—Mospilan SG, Folicur, their combination, and a negative control — with 10 cages per treatment. Adult bees of both species will be exposed to the spray treatments for a minimum of 7 days and various endpoints regarding fitness (i.e., survival and reproduction) as well as foraging behavior of the two species and pollination success will be assessed. The results of this experiment will provide information on whether the spray treatments differentially affect the generalist species O. bicornis and the closely related oligolectic species O. brevicornis , and on any interactions between the insecticide and the fungicide at realistic exposure levels.