Urban landscapes tend to increase the presence of pathogenic protozoa, microsporidia and viruses, but likely decrease the abundance of viruses in wild bees and wasps

Pathogens are shared between wild bees and wasps but little is known about how urbanization affects their occurrence. Here, the role of temperature and fragmentation of green areas, both associated with urbanization, in modulating pathogen loads was investigated. Twelve pathogens were investigated in the bees Anthophora plumipes Pallas, 1772, Halictus scabiosae (Rossi, 1790), Osmia cornuta (Latreille, 1805), and the wasp Polistes dominula (Christ, 1791) sampled across an urbanization gradient in a metropolitan area of northern Italy. Overall, the relative presence/abundance of the pathogens were found to be species specific, as were the responses to urbanization. Anthophora plumipes and O. cornuta had a higher occurrence probability of the neogregarine protozoan Apicystis bombi in more fragmented urban areas. In the same bee species, both temperature and the fragmentation of green areas reduced the number of copies of the deformed wing virus (DWV). In H. scabiosae and P. dominula, higher temperature increased respectively the likelihood of occurrence of DWV and chronic bee paralysis virus (CBPV). In addition, the viruses were found to be replicative in all samples tested. The results show a consistent presence of pathogens in the four target species, and that urbanization plays a role in modulating the pathogen load. Although transmission pathways could not be considered here, it may be suggested that appropriate management of urban areas may buffer wild insects from potentially harmful pathogens. Whether the presence of such pathogens also results in symptomatic phenotypes remains to be determined in laboratory experiments.