How acetic acid alters interactions of parasitoids with their Drosophila melanogaster hosts.

Drosophila melanogaster, the common fruit fly, is frequently infected by parasitic wasps in nature. Flies have a cellular immune response to encapsulate and kill wasp eggs, but this can be suppressed by injected wasp venom. Flies also display defensive behaviors to prevent infection or cure themselves once infected. For example, it was previously shown that parasitized fly larvae, which live in rotting fruits, medicate themselves by consuming more alcohol. Acetic acid is another potentially toxic product of fermentation sought out by D. melanogaster. Here, we test whether acetic acid is beneficial to flies by affecting wasp parasitism. We performed infections on D. melanogaster using two parasitic wasp species, a generalist and a specialist, and measured parasitism rates in acetic acid, parasitism rates after longterm exposure to acetic acid, fly and wasp tolerance of acetic acid, and fly substrate choice with various levels of acetic acid. Our data indicate that acetic acid can protect fly larvae from infection in some scenarios.