*Systematic Review* **Pathogens Spillover from Honey Bees to Other Arthropods**

**Antonio Nanetti, Laura Bortolotti \* and Giovanni Cilia**

Council for Agricultural Research and Agricultural Economics Analysis, Centre for Agriculture and Environment Research (CREA-AA), Via di Saliceto 80, 40128 Bologna, Italy; antonio.nanetti@crea.gov.it (A.N.); giovanni.cilia@crea.gov.it (G.C.)

**\*** Correspondence: laura.bortolotti@crea.gov.it; Tel.: +39-051-353103

**Abstract:** Honey bees, and pollinators in general, play a major role in the health of ecosystems. There is a consensus about the steady decrease in pollinator populations, which raises global ecological concern. Several drivers are implicated in this threat. Among them, honey bee pathogens are transmitted to other arthropods populations, including wild and managed pollinators. The western honey bee, *Apis mellifera*, is quasi-globally spread. This successful species acted as and, in some cases, became a maintenance host for pathogens. This systematic review collects and summarizes spillover cases having in common *Apis mellifera* as the mainteinance host and some of its pathogens. The reports are grouped by final host species and condition, year, and geographic area of detection and the co-occurrence in the same host. A total of eighty-one articles in the time frame 1960–2021 were included. The reported spillover cases cover a wide range of hymenopteran host species, generally living in close contact with or sharing the same environmental resources as the honey bees. They also involve non-hymenopteran arthropods, like spiders and roaches, which are either likely or unlikely to live in close proximity to honey bees. Specific studies should consider host-dependent pathogen modifications and effects on involved host species. Both the plasticity of bee pathogens and the ecological consequences of spillover suggest a holistic approach to bee health and the implementation of a One Health approach.

**Keywords:** spillover; inter-species transmission; honey bee diseases; pathogens; virus; bacteria; microsporidia; *Nosema*; trypanosomatids; wild bees; arthropods; Hymenoptera
