Sclerotization Protects Drosophila nigrospiracula against Parasitism by Ectoparasitic Mites

AbstractThe cuticle of arthropods provides the first line of defense against predators, pathogens, and parasites. While most studies focus on the role of cuticular defense against microbial pathogens, few have examined whether the cuticle protects against parasites. Here, we investigate the relative importance of cuticular sclerotization and behavioral defenses in Drosophila nigrospiracula against an ectoparasite (Macrocheles subbadius). We first tested whether newly eclosed (NE; i.e., teneral) flies are more susceptible to parasitism than fully sclerotized (FS) flies. In a separate experiment, we severed the wings to test whether the differential susceptibility between NE and FS flies was explained by wing-mediated defenses. We also performed endurance (negative geotaxis) assays to determine whether reduced physical endurance among NE flies contributed to higher vulnerability to parasitism. We found that regardless of whether wings were intact or removed, the prevalence and intensity of infection was significantly higher among NE flies than among FS flies. The negative geotaxis assay also showed that NE flies had lower endurance than FS flies. Moreover, differences in the probability and severity of parasitism between NE and FS flies were magnified when the wings were removed. These results suggest that while cuticular sclerotization serves as the primary first line of defense, wing-mediated behaviors likely allow flies to avoid or minimize mite attacks, and the effectiveness of these behaviors is likely limited by physical endurance. Differences in morphology and behavior between immature adults (not FS) and mature organisms (FS) may drive variation in parasitism risk across developmental stages.