The development of immunity in a social insect: evidence for the group facilitation of disease resistance.

The extraordinary diversity and ecological success of the social insects has been attributed to their ability to cope with the rich and often infectious microbial community inhabiting their nests and feeding sites. Mechanisms of disease control used by eusocial species include antibiotic glandular secretions, mutual grooming, removal of diseased individuals from the nest, and the innate and adaptive immune responses of colony members. Here we demonstrate that after a challenge exposure to the entomopathogenic fungus Metarhizium anisopliae, dampwood termites Zootermopsis angusticollis have higher survivorship when individuals develop immunity as group members. Furthermore, termites significantly improve their ability to resist infection when they are placed in contact with previously immunized nestmates. This "social transfer" of infection resistance, a previously unrecognized mechanism of disease control in the social insects, could explain how group living may improve the survivorship of colony members despite the increased risks of pathogen transmission that can accompany sociality.