Global invasion risk of Apocephalus borealis, a honey bee parasitoid
Apocephalus borealis is a cryptic parasitoid of hymenopterans native to North America that parasitizes honey bees (Apis mellifera) and is associated with infested bees absconding the hive and dying outside. The flies can also harbour viral infections and nosematosis. Recently, nucleotide sequences identical to A. borealis were reported from bulk screenings of honey bees from Belgium and South Korea, although no adult flies have been collected. To predict the potential invasion risk of A. borealis across the world, we constructed a MaxEnt species distribution model based on occurrence data from North America submitted to the citizen science project ZomBee Watch (zombeewatch.org). We show that extensive parts of Europe, the Mediterranean Basin, Asia Minor, southern Africa, eastern Asia, Australasia, and North and South America show high degrees of climatic suitability for invasion, suggesting that the fly could establish in these regions. The potential invasion range is expected to stay similar under different climate change scenarios. We discuss the status of A. borealis as an invasive species and measures that can be taken to reduce the risk of its introduction outside of North America. Our results highlight A. borealis as a potential threat to honey bee health worldwide that requires urgent attention of international veterinary bodies to prevent its spread.