Covert infections with a honeybee 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 in the past decades. Ants have long been hypothesised 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 measurements, viral replication assays, and host immune gene expression analyses to test whether the clonal raider ant Ooceraea biroi can harbour and transmit ABPV. ABPV-injected ants showed delayed development and elevated mortality. Although we found no evidence of viral replication, the virus was able to spread among colony members and viral particles persisted in colonies for several days. These results show that ants can acquire ABPV, incur fitness costs, and pass 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 could contribute to their environmental persistence and spillover across species.