Abstract
Age-grading techniques were applied to natural horn fly populations, Haematobia irritans irritans , collected from beef cattle in central Iowa, USA, in 1979 and 1980. Fly population densities were estimated 3 or 4 times weekly by counting the flies on 1 side of each of 15 cattle in 1979 and 7 cattle in 1980. Flies were sampled with sweep nets and subsequently sexed and age-graded. Nine gonotrophic age groups were recognized and used to study seasonal demographic changes in adult horn fly populations. A stable age distribution was observed among the flies on a semi-isolated herd of 25 cattle, but when the cattle were moved near a much larger number of insecticide-treated, horn fly-free animals, a catastrophic decline in population occurred and age structure and density fluctuated thereafter. Recruitment of teneral adults occurred through October, although population density declined. Horn fly adults were not detected after November. Sampling bovine dung showed horn fly yields that correlated with adult densities. Adult male survival rates were ca. 95% of the female survival rate. Estimates were obtained of horn fly recruitment and emigration rates.
Published Version
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