Abstract Parasites represent one of the main threats to all
organisms and are likely to be particularly significant for
social animals because of the increased potential for
intragroup transmission. Social animals must therefore have
effective resistance mechanisms against parasites and one
of the most important components of disease resistance in
ants is thought to be the antibiotic-producing metapleural
gland. This gland is ancestral in ants, but has been lost
secondarily in a small number of species. It is unknown
whether these evolutionary losses are due to a reduction in
parasite pressure or the replacement of the gland’s function
with other resistance mechanisms. Here we used the
generalist entomopathogenic fungus Metarhizium to compare
the disease resistance of a species of a weaver ant,
Polyrhachis dives, which has lost the metapleural gland,
with that of the well-studied leaf-cutting ant Acromyrmex
echinatior and two other ant species, Myrmica ruginodis
and Formica fusca, all of which have metapleural glands.
The P. dives weaver ants had intermediate resistance when
kept individually, and similar resistance to A. echinatior
leaf-cutting ants when kept in groups, suggesting that the
loss of the metapleural gland has not resulted in weaver
ants having reduced disease resistance. P. dives weaver ants
self-groomed at a significantly higher rate than the other
ants examined and apparently use their venom for resistance,
as they had reduced resistance when their venom
gland was blocked and the venom was shown in vitro to
prevent the germination of fungal spores. Unexpectedly, the
leaf-cutting ant A. echinatior also had reduced resistance to
Metarhizium when its venom gland was blocked. It
therefore appears that the evolutionary loss of the metapleural
gland does not result in reduced disease resistance
in P. dives weaver ants, and that this at least in part may be
due to the ants having antimicrobial venom and high selfgrooming
rates. The results therefore emphasise the
importance of multiple, complementary mechanisms in the
disease resistance of ant societies.