2nd Place: Quit bugging me: The influence of phorid flies on foraging and immunity in fire ant workers

Host—parasitoid interactions are complex. A parasitoid can change its host’s behavior by direct infection or simply by its presence in the shared environment. In the red imported fire ant (RIFA, Solenopsis invicta), workers display defensive postures to avoid potential parasitism when parasitoid fire ant decapitating flies (Pseudacteon spp.) hover above them. We investigated the genetic factors related to nocturnal foraging shift behavior at the colony level. By quantifying expression of the RIFA foraging gene (Sifor) and immune genes of colonies exposed to decapitating flies and control colonies, we aimed to provide information on the molecular processes related to change in foraging behavior of RIFA. In RIFA, Sifor is shown to correlate with worker task. Odorant-binding protein 11 (OBP-11) and the antimicrobial peptides hymenoptaecin (hym), abaecin, and defensin-2 (def-2) have been shown to be significantly more highly expressed in foragers than in nurses. We also explored cytochrome P450 4C1-like (CYP4C1) expression as it is thought to play a role in immunity of ants. These genes are hypothesized to experience varying expression between workers and nurses due to environmental differences. Although colonies exposed to parasitoids foraged less than control colonies (flies absent), they did not experience significant changes in Sifor, OBP-11, abaecin, or CYP4C1, however, these colonies showed a significant increase of hym and def-2. These results allude to the complexity of host—parasitoid interactions in RIFA colonies.