The Drosophila testacea species group belongs to the Immigrans-tripunctata radiation of the subgenus Drosophila, and contains 4 species: Drosophila putrida, Drosophila neotestacea, Drosophila testacea, and Drosophila orientacea. Testacea species are specialist mushroom-feeding flies, and can metabolize toxic compounds in Amanita mushrooms. The Testacea species group is studied for its specialist ecology, population genetics, and bacterial endosymbionts. The North American species Drosophila neotestacea is perhaps the best-studied of the group for its interactions with parasitic wasps and nematodes, bacterial endosymbionts, and trypanosomatid parasites. Of note, selfish X chromosomes have been discovered in three of the four Testacea group species.