Trophallaxis and prophylaxis: Social immunity in the carpenter ant Camponotus pennsylvanicus

Group behaviour can increase disease resistance among nestmates and generate social prophylaxis. Stomodeal trophallaxis, or mutual feeding through regurgitation in social insects, may boost colony-level immunocompetence. We provide evidence for increased trophallactic behaviour among immunized workers of the carpenter ant Camponotus pennsylvanicus, which, together with increased antimicrobial activity of the regurgitate droplet, help explain the improved survival of droplet recipient ants relative to controls following an immune challenge. We have identified a protein related to cathepsin D, a lysosomal protease, as a potential contributor to the antimicrobial activity. The combined behavioural and immunological responses to infection in these ants likely represent an effective mechanism underlying the social facilitation of disease resistance, which could potentially produce socially-mediated colony-wide prophylaxis. The externalization and sharing of an individual’s immune responses via trophallaxis could be an important component of social immunity, allowing insect colonies to thrive under high pathogenic pressures.