title: Wood ants produce a potent antimicrobial agent by applying formic acid on tree-collected resin.
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 fungusMetarhizium brunneumafter 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.
authors.affiliation: Department of Ecology and Evolution University of Lausanne Biophore, UNIL-Sorge Lausanne Switzerland.
authors.forename: Timothée
authors.initials: T
authors.lastname: Brütsch
authors.affiliation: Department of Ecology and Evolution University of Lausanne Biophore, UNIL-Sorge Lausanne Switzerland; FARCE Institute of Biology University of Neuchâtel Neuchâtel Switzerland.
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Jaffuel
authors.affiliation: Institute of Chemistry NPAC University of Neuchâtel Neuchâtel Switzerland.
authors.forename: Armelle
authors.initials: A
authors.lastname: Vallat
authors.affiliation: FARCE Institute of Biology University of Neuchâtel Neuchâtel Switzerland.
authors.forename: Ted C J
authors.initials: TC
authors.lastname: Turlings
authors.affiliation: Department of Ecology and Evolution University of Lausanne Biophore, UNIL-Sorge Lausanne Switzerland.
authors.forename: Michel
authors.identifier: 0000-0001-7207-199X
authors.initials: M
authors.lastname: Chapuisat
keywords: Formica; antimicrobials; ants; chemical defenses; formic acid; fungal pathogen; social insects; tree resin