Social transmission of immunity in the carpenter ant Camponotus pennsylvanicus

Social insects exploit microbially-rich environments, nesting and foraging in soil, leaf litter, and/or decayed wood. Risk of disease transmission is particularly acute in their densely-populated colonies, and they use a variety of defense mechanisms to cope with disease, including immunological responses. In this study, the carpenter ant Camponotus pennsylvanicus was used as a model system to investigate transfer of immunity among nestmates via mouth-to-mouth regurgitation (trophallaxis). These ants store nutrients in their crop and engage regularly in trophallaxis, feeding all colony members through this Òsocial stomachÓ. We hypothesize that in addition to nutrients, ants may also be transferring immune proteins and/or immune elicitors via these frequent social exchanges. To induce an immune response, workers were exposed to a lethal dose, to de-activated pathogen solution, or to pathogen-free control solution of either the bacteria Serratia marcescens or the entomopathogenic fungus Metarhizium anisopliae. To determine the presence of novel immune proteins, regurgitate droplets taken during trophallaxis one to two days post-treatment were analyzed with SDS-PAGE.  Our preliminary results indicate the presence of  novel proteins in the crop of immunized ants and provide the first evidence that social transmission of immunity may occur during trophallaxis. Future research will include SDS-PAGE assays of hemolymph, fat tissue, and salivary glands to pinpoint the source and identity of these proteins.