Experimental cross species transmission of a major viral pathogen in bees is predominantly from honeybees to bumblebees

Cross-species transmission of a pathogen from a reservoir to a recipient
host species, spillover, can have major impacts on biodiversity, domestic
species and human health. Deformed wing virus (DWV) is a panzootic RNA
virus in honeybees that is causal in their elevated colony losses, and
several correlative field studies have suggested spillover of DWV from
managed honeybees to wild bee species such as bumblebees. Yet unequivocal
demonstration of DWV spillover is lacking whilst spillback, the
transmission of DWV from a recipient back to the reservoir host, is rarely
considered. Here we show in fully crossed laboratory experiments that
transmission of DWV (genotype A) from honeybees to bumblebees occurs
readily, yet we neither detected viral transmission from bumblebees to
honeybees nor onward transmission from experimentally infected to
uninoculated bumblebees. Our results support the potential for viral
spillover from honeybees to other bee species in the field when robbing
resources from heterospecific nests or when visiting the same flowers.
They also underscore the importance of studies on the virulence of DWV in
wild bee species so as to evaluate viral impact on individual and
population fitness as well as viral adaption to new host species.