VARIATION IN POPULATION-DENSITY OF THE FACE FLY, MUSCA-AUTUMNALIS DEGEER (DIPTERA, MUSCIDAE), AMONG SELECTED BREEDS OF BEEF-CATTLE

Statistically significant differences existed in weekly population est imates of the face fly, Musca autumnalis De Geer, on purebred Angus, C harolais, Chianina, Hereford, Polled Hereford and Red Poll beef cattle . Host selection by the flies caused inconsistent differences in breed means from week to week during each year of the 3-yr study. Inconsist ent host selection by the face fly population also occurred on individ ual cows within each breed preventing classification of cows as either fly-resistant or fly-susceptible. Although Charolais and Chianina cow s had approximately the same mean numbers of face flies as the Angus, Hereford, Polled Hereford, and Red Poll cows, they required no treatme nt for pinkeye during the 3-yr study. Chi-square analysis showed that for the breeds requiring pinkeye treatments, the percentage of treated cows differed significantly among breeds in 1989 and 1990. In 1988, 1 989, and 1990, there were 56, 83, and 57% of Hereford cows, respective ly, that required treatment for pinkeye. Factors other than host face color appeared to be involved in the selective interaction between the face fly and the cattle breeds used in this study. No significant ind irect effect of the dam face fly population density on calf weaning we ight was determined.