Ectoparasites are ubiquitous and can impose significant fitness costs on their host. Our current knowledge of the physiological and structural defense mechanisms of invertebrate hosts during ectoparasite infection is limited. This lack of understanding poses a major obstacle to understanding ectoparasite resistance mechanisms and their genetic basis. The present study aims to address this imbalance by investigating post-attachment adaptations in Drosophila that mitigate the costs of ectoparasitism by mites, Gamasodes pachysetis (Parasitidae). We found that different species of Drosophila co-occurring with this mite in nature varied in mite attachment duration, suggesting a (broad-sense) genetic basis to post-attachment defensive traits. Flies of a given species that were experimentally pre-infected by mites exhibited reduced attachment durations compared to naïve flies. This response was not repeatable in flies that were experimentally wounded with a surgical device to mimic mite-induced cuticle damage, suggesting that specific protective factors are induced by mite attachment and are specific responses to feeding mites. Resistance assays on a panel of UAS-GAL4 transgenic lines identified candidate genes that may be responsible for differences in attachment duration. The results support the hypothesis that flies possess specific physiological mechanisms that interact with feeding mites, and that such factors mediate the duration of mite attachment. The inter-specific variation in the ability to shed mites suggests that different species have evolved the differential ability to mitigate the effects of ectoparasitsm by Gamasodes mites and, by extension, implies the existence of within-population genetic variation in mite resistance.
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