Parasite preferences for large host body size can drive overdispersion in a fly-mite association.

Body size generally correlates intraspecifically with insect fitness but can also correlate with parasite abundance (number of parasites). Host preferences by parasites, and variation in host immunity, could contribute to this trend. We investigated the effect of host size on mite-fly interactions (Macrocheles subbadius and Drosophila nigrospiracula). Mites strongly preferred to infect larger flies in pair-wise choices, and larger flies were more likely to be infected and acquired more mites in infection microcosms. Preferences of parasites resulted in size-biased infection outcomes. We discuss the implications of this heterogeneity in infection on parasite overdispersion and fly populations.