Is Osmia bicornis an adequate regulatory surrogate? Comparing its acute contact sensitivity to Apis mellifera.

Bees provide essential ecosystem services and help maintain floral biodiversity. However, there is an ongoing decline of wild and domesticated bee species. Since agricultural pesticide use is a key driver of this process, there is a need for a protective risk assessment. To achieve a more protective registration process, two bee species, Osmia bicornis/Osmia cornuta and Bombus terrestris, were proposed by the European Food Safety Authority as additional test surrogates to the honey bee Apis mellifera. We investigated the acute toxicity (median lethal dose, LD50) of multiple commercial insecticide formulations towards the red mason bee (O. bicornis) and compared these values to honey bee regulatory endpoints. In two thirds of all cases, O. bicornis was less sensitive than the honey bee. By applying an assessment factor of 10 on the honey bee endpoint, a protective level was achieved for 87% (13 out 15) of all evaluated products. Our results show that O. bicornis is rarely an adequate additional surrogate species for lower tier risk assessment since it is less sensitive than the honey bee for the majority of investigated products. Given the currently limited database on bee species sensitivity, the honey bee seems sufficiently protective in acute scenarios as long as a reasonable assessment factor is applied. However, additional surrogate species can still be relevant for ecologically meaningful higher tier studies.