Experimental infections with a honey bee virus induce fitness costs in ant colonies

Acute bee paralysis virus (ABPV) is a key driver of honey bee colony losses that has been increasingly reported in non-bee hosts. Ants have long been hypothesized to act as viral reservoirs, but most evidence comes from field surveys and experimental tests are still scarce. Here, we combined survival and transmission assays, viral load quantification and viral replication assays following experimental inoculations to test whether the clonal raider ant Ooceraea biroi can harbour and transmit ABPV within its colonies. ABPV-injected immatures and adults showed delayed development and elevated mortality, respectively. Viral replication assays suggested these fitness costs were caused by host responses (e.g. immunopathology) rather than viral replication. Viral particles persisted for days in inoculated ants, and high viral loads were detected in untreated colony members after 1-3 days of cohabitation with ABPV-injected pupae or adults, indicating rapid viral spread. These results show that ants can acquire ABPV, incur fitness costs and pass on the virus within their colonies, suggesting that they may act as incidental viral reservoirs. By maintaining and disseminating honey bee viruses, even without supporting replication, ants may contribute to their environmental persistence and spillover across species.