Alcohol Consumption as Self-Medication against Blood-Borne Parasites in the Fruit Fly

SummaryPlants and fungi often produce toxic secondary metabolites that limit their consumption [1, 2, 3 and 4], but herbivores and fungivores that evolve resistance gain access to these resources and can also gain protection against nonresistant predators and parasites [3, 5, 6, 7 and 8]. Given that Drosophila melanogaster fruit fly larvae consume yeasts growing on rotting fruit and have evolved resistance to fermentation products [ 9 and 10], we decided to test whether alcohol protects flies from one of their common natural parasites, endoparasitoid wasps [ 11, 12 and 13]. Here, we show that exposure to ethanol reduces wasp oviposition into fruit fly larvae. Furthermore, if infected, ethanol consumption by fruit fly larvae causes increased death of wasp larvae growing in the hemocoel and increased fly survival without need of the stereotypical antiwasp immune response. This multifaceted protection afforded to fly larvae by ethanol is significantly more effective against a generalist wasp than a wasp that specializes on D. melanogaster. Finally, fly larvae seek out ethanol-containing food when infected, indicating that they use alcohol as an antiwasp medicine. Although the high resistance of D. melanogaster may make it uniquely suited to exploit curative properties of alcohol, it is possible that alcohol consumption may have similar protective effects in other organisms.

► Environmental ethanol protects D. melanogaster from being parasitized by wasps
► Consumption of ethanol by D. melanogaster also kills internal wasp parasites
► D. melanogaster choose high ethanol content food when infected by wasps
► Protection afforded to flies by ethanol is stronger against a generalist parasite