The effect of <i>Macrocheles muscaedomesticae</i> and <i>M. subbadius</i> (Acarina: Macrochelidae) phoresy on the dispersal of <i>Stomoxys calcitrans</i> (Diptera: Muscidae)

Abstract

In south-central Ontario, the stable flies disperse from their overwintering farms and re-establish populations at neighbouring dairy and beef farms each spring. Two species of phoretic macrochelid mites commonly found on stable flies are Macrocheles muscaedomesticae and M. subbadius. We tested the hypothesis that mite phoresy affects the dispersal of their stable fly phorionts. At a beef farm we found a higher proportion of parous stable flies with mite scars than expected, based on the proportion of nulliparous females carrying mites. These results were consistent with our hypothesis, indicating that stable flies without mites may be emigrating more than flies carrying mites. We further tested our hypothesis by comparing the mite load on dispersing stable flies sampled with a vehicle-mounted truck trap to the mite load on resident stable flies sampled from three dairy farms and one beef farm (May to October, 2001). Significantly, no stable flies caught in the truck trap were carrying mites, compared to the seasonal means of 10% and 5% of female and male stable flies with mites at the four farms. This effect of mite phoresy on stable fly populations is discussed.