No evidence for behavioral immunity against a viral pathogen in the invasive fire ant Solenopsis invicta Buren (Hymenoptera: Formicidae)

Social insects manage diseases using various behavioral strategies including hygienic behavior, discrimination of infected individuals and/or organizational segregation (e.g., reduced interactions between high-risk foragers with high-value colony members including queen and brood). While such behaviors have been demonstrated to reduce the spread of fungal pathogens in ants, whether ant colonies respond to viral infection via similar behavioral mechanisms remains untested. Using Solenopsis invicta virus 3 (SINV-3) and its ant host, the red imoported fire ant (Solenopsis invicta) as the model system, we test if 1) uninfected workers discriminate against infected nestmates; 2) worker nest-bound flow (i.e., the numbers if workers entering the opening of a nest cell from foraging arena) is reduced when colonies are challenged with SINV-3; and 3) infected colonies alter macronutrients intakes and foraging intensity. We also monitored the viral infection status of nurse workers in the nest cell throughout entire experiments. Our results showed that infected workers were not discriminated against and that the nest-bound flow was comparable before and after colonies being challenged by SINV-3. Coupled with the finding of widespread SINV-3 infection in ants in the nest cell upon experiment termination, these results suggest the inability of fire ant colonies to detect and respond to SINV-3 infection. However, we found SINV-3-infected colonies foraged significantly less than uninfected conspecifics yet increased their intake on protein-rich diet. We discuss the potential adaptive value of such behavioral changes on infected fire ant colonies and how virus-host interaction shapes viral dynamics in fire ant population.