Viruses and their effects in ants (Hymenoptera: Formicidae)

Viruses are ubiquitous within all forms of cellular life, including ants. We documented the currently known viral infections described and their effects on ants. Our literature review found 87 different viruses (including 40 putative viruses and five bacteriophages detected via high-throughput sequencing) across 38 ant species. The majority of these viruses have been described from studying pathogens as potential biological control agents for the invasive red imported fire ant, Solenopsis invicta BUREN, 1972 or due to efforts to determine if ants serve as reservoirs for honey bee viruses in places where Argentine ants, Linepithema hutnile (MAYR, 1868) are also invasive. Most of these viruses belong to the Picornavirales order of small RNA single-stranded RNA (ssRNA) viruses, with more than half being positive -sense (+ssRNA) viruses. We review modes of viral transmission and suggest that horizontal transmission is a common mode of infection in ants as they share food via trophallaxis, although vertical transmission of viruses in eggs from queens has been observed. Viruses can substantially alter ant behaviour and physiology. We review effects of viruses on immune gene expression, feeding, locomotion, aggression, and colony defence. Then, we review the current state of the art in prospecting and using viruses for biological control. Mortality of ant colonies can occur, although the impact of some viral infections appears to be dependent on other environmental factors. Solenopsis invicta virus 3 (SINV-3) has had the most focus as a biological control agent. Effective laboratory and field transmission of SINV-3 in S. invicta colonies has been demonstrated although large-scale ant control with SINV-3 has not yet been reported. Finally, we review virus discovery and detection methods, including high-throughput sequencing that has revolutionised the field. We encourage testing for viral replication within each ant species to confirm active infection and that the ant is a true host to the virus, and we recommend approaches for viral discovery in invasive ants that focus on colony monitoring in their native range.