The natural histories of parasites and their hosts are intertwined, and intensity of parasitism depends on parasite abundance and host behavior as well as potential effects of sex/age. To characterize potential effects of parasite abundance and host sex/age on chigger mite (Eutrombicula alfreddugesi) ectoparasitism on Eastern Fence Lizards (Sceloporus undulatus), we measured 1) the abundance of mites in the environment as well as mite load and prevalence on lizards throughout the activity season, 2) sex- and age-specific patterns of ectoparasitism, and 3) week-to-week consistency of mite loads on lizards. Environmental mite abundance varied seasonally in close association with mean monthly temperatures and was the main driver of pronounced seasonal variation in mite loads on lizards. Mite loads were almost always higher on yearlings than on adults and, somewhat unexpectedly, were never higher on adult males than any of the other age-sex classes. As adults, females had higher mite loads than did males in June–July, but as yearlings, males had higher mite loads than did females in July–September. Despite considerable week-to-week variation, rank-ordering of lizard mite loads was highly consistent. These findings indicate that 1) consistent, age-specific sex biases are superimposed on strong seasonal variation in mite loads, and 2) detrimental effects of mites are expected to be consistently stronger in some individuals than in others.

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