Social groups are at particular risk for parasite
infection, which is heightened in eusocial insects by the low
genetic diversity of individuals within a colony. To combat
this, adult ants have evolved a suite of defenses to protect each
other, including the production of antimicrobial secretions.
However, it is the brood in a colony that are most vulnerable
to parasites because their individual defenses are limited, and
the nest material in which ants live is also likely to be prone to
colonization by potential parasites. Here, we investigate in
two ant species whether adult workers use their antimicrobial
secretions not only to protect each other but also to sanitize the
vulnerable brood and nest material.We find that, in both leafcutting
ants and weaver ants, the survival of the brood was
reduced and the sporulation of parasitic fungi from them
increased, when the workers nursing them lacked functional
antimicrobial-producing glands. This was the case for both
larvae that were experimentally treated with a fungal parasite
(Metarhizium) and control larvae which developed infections
of an opportunistic fungal parasite (Aspergillus). Similarly,
fungi weremore likely to grow on the nest material of both ant
species if the glands of attending workers were blocked. The
results show that the defense of brood and sanitization of nest
material are important functions of the antimicrobial secretions
of adult ants and that ubiquitous, opportunistic fungi
may be a more important driver of the evolution of these
defenses than rarer, specialist parasites.