Abstract
Wood ants fight pathogens by incorporating tree resin with antimicrobial properties into their nests. They also produce large quantities of formic acid in their venom gland, which they readily spray to defend or disinfect their nest. Mixing chemicals to produce powerful antibiotics is common practice in human medicine, yet evidence for the use of such “defensive cocktails” by animals remains scant. Here, we test the hypothesis that wood ants enhance the antifungal activity of tree resin by treating it with formic acid. In a series of experiments, we document that (i) tree resin had much higher inhibitory activity against the common entomopathogenic fungus Metarhizium brunneum after having been in contact with ants, while no such effect was detected for other nest materials; (ii) wood ants applied significant amounts of endogenous formic and succinic acid on resin and other nest materials; and (iii) the application of synthetic formic acid greatly increased the antifungal activity of resin, but had no such effect when applied to inert glass material. Together, these results demonstrate that wood ants obtain an effective protection against a detrimental microorganism by mixing endogenous and plant‐acquired chemical defenses. In conclusion, the ability to synergistically combine antimicrobial substances of diverse origins is not restricted to humans and may play an important role in insect societies.
Highlights
Animals living in large social groups are exposed to a high risk of epidemics
We tested whether spruce tree resin that had been in contact with wood ants had increased inhibitory activity against the generalist entomopathogenic fungus Metarhizium brunneum, compared to resin that had not been contacted by ants
We show that wood ants enhance the antifungal activity of tree-collected resin by supplementing it with endogenous
Summary
Animals living in large social groups are exposed to a high risk of epidemics. In response to this threat, social animals have evolved sophisticated individual and collective means to control disease,. Collective defenses include ways to keep the environment hygienic, for example, by removing or neutralizing infectious particles (Morelos-Juárez, Walker, Lopes, & Hughes, 2010; Tragust et al, 2013) Formic acid is effective against Metarhizium, a common fungal pathogen of ants (Graystock & Hughes, 2011), and is used by Lasius neglectus ants to disinfect their brood (Tragust et al, 2013). This suggests that wood ants may combine endogenous acids with tree resin. We examined whether (i) ants enhance the antifungal activity of resin, (ii) ants add endogenous acids to resin, and (iii) these acids increase the antifungal activity of resin
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