Hosts use a variety of strategies to deal with a never ending battle with its parasites. Larvae of Drosophila species are often infected by parasitoid wasps and feeding by the wasp larvae lead to the eventual death of fly larvae. A recent study by Milan et al. (2012) published in Current Biology shows that fly larvae take advantage of environmental alcohols to limit the infection of parasitoid wasp larvae. The work shows that consumed alcohol leads to the death of the wasp larvae. In addition, Drosophila larvae seek out alcohol when infected by the parasite in an effort to self-medicate itself against the invader. How this story develops will be interesting in light of the well-known polymorphism in the alcohol dehydrogenase gene in Drosophila melanogaster. It will be interesting to know if the different alleles of Adh change the effectiveness of the self-medication or the behavior.
Plants and fungi often produce toxic secondary metabolites that limit their consumption [1-4], but herbivores and fungivores that evolve resistance gain access to these resources and can also gain protection against nonresistant predators and parasites [3, 5-8]. Given that Drosophila melanogaster fruit fly larvae consume yeasts growing on rotting fruit and have evolved resistance to fermentation products [9, 10], we decided to test whether alcohol protects flies from one of their common natural parasites, endoparasitoid wasps [11-13]. 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.