Surprisingly, there was no significant interaction in either
ant species between gland blockage and Metarhizium exposure.
Antimicrobial secretions have previously been shown to
be very important for protecting adult leaf-cutting ants and
weaver ants against exposure to the Metarhizium parasite
(Poulsen et al. 2002; Graystock and Hughes 2011), as well
as for protecting brood of L. neglectus ants (Tragust et al.
2013). The lack of a significant interaction here between gland
blockage and Metarhizium exposure is likely to be for two
reasons. First, both the probability of parasite infection success
and the effects of antimicrobial secretions are dosedependent
(Ebert et al. 2000; Hughes et al. 2004a; Stow
et al. 2007; Turnbull et al. 2012). The greater the dose of the
parasite strain, the more likely an infection is to be successful,
and it may be that the dose of the parasite strain used here was
too high for the antimicrobial secretions that were transferred
from the adult ants to be fully effective in defending brood
against the Metarhizium parasite. In addition, lower doses of
antimicrobial compounds are less likely to be effective against
a parasite and it may be that the dose of antimicrobial secretions
transferred to the brood was too low to fully defend the
brood against Metarhizium and, thus, too low for a strong
effect of gland blockage on resistance to Metarhizium to be
seen. Second, the effect of gland blockage on the mortality of
even the control brood was relatively high. Both here and in
other studies (Poulsen et al. 2002; Graystock and Hughes
2011), little impact of gland blockage on control adult ants
themselves has been found, but it appears that control brood
are far more susceptible to the impact of being with nursing
workers with blocked glands. The behavior of the nursing
workers, including their grooming of the brood, was unchanged
by gland blockage, and there is no known nutritional
role for the glandular secretions, so it seems most probable
that this impact relates to the infections by opportunistic
fungal parasites which developed.