FIGURE 1.

Graphical representation of the natural routes of inter- and intra-species transmission of viruses found in Hymenoptera. Transmission routes that are more likely to occur are represented by solid arrows, transmission routes that are less likely or less frequently observed are represented by dotted arrows. The most likely route of inter-species transmission is through the use of shared flowers (Singh et al., 2010; Alger et al., 2019), depicted in the middle surrounded by a red dotted line. Inter- and intra-species transmission in non-social bees, depicted on the left side can occur through contact at nest aggregations or the reuse of virus-contaminated old nest cavities (Krunicì and Stanisavljevicì, 2006). In social bees, depicted on the right side, the main intra-species transmission route is likely, via intense contact in the nest. Social behavior such as trophallaxis and body contact could mediate transmission (Amiri et al., 2014, 2019; Chen et al., 2014; Coulon et al., 2018 and others, see main text). Further intra-species transmission can also occur via vectors, for honey bees this is a very important transmission route for several viruses, mediated by V. destructor (Santillán-Galicia et al., 2010; Möckel et al., 2011; Gisder et al., 2018; Posada-Florez et al., 2019; Ryabov et al., 2019 and others, see main text). Intra-and inter-species transmission via vectors, other than V. destructor [e.g., the small hive beetle, phorid flies (Eyer et al., 2009; Core et al., 2012; Menail et al., 2016)] are less frequent. Robbing and drifting are also two potential routes of inter- and intra-species transmission, respectively, described in social bees. Yet their role in virus transmission is likely to be minor compared to other transmission routes. Lastly, social parasitism creates a high contact between individuals from different species and hence is likely to facilitate virus transmission, in social bees. Inter-species transmission in Vespidae sp. can occur through feeding on infected Hymenoptera, or other insects that are infected with a virus or contain the virus on their exterior (Loope et al., 2019). Another potential transmission route for wasps is the use of shared contaminated flowers (Mordecai et al., 2016b). Intra-species transmission in social Vespidae sp. is also likely to occur via intense contact within the nest.