A Comparison of Methods for Assessing Age Structure and Abundance in Populations of Nondiapausing Female Musca Autumnalis (Diptera: Muscidae)

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Abstract
Samples of female face flies, Musca autumnalis, were simultaneously collected from a haltered steer, a blood-smeared board, and cylindrical white sticky traps. The 3 methods yielded samples equivalent in (1) gonadotrophic age of nonparasitized females, and in (2) the frequency of different life stages of the nematode Heterotylenchus autumnalis within parasitized flies. However, gravid nonparasitized flies were seriously undersampled with all methods, and a suspicious deficit of nulliparous flies suggested that this age group had also been undersampled. Within the same day, the age composition of samples did not vary significantly with time of collection from traps. The within-day efficiency of the sticky traps varied with air temperature. A method of correcting for this source of bias is presented. A comparison of face counts from cattle to concurrently derived catch rates (females/h) from traps revealed that the former were insensitive to large changes in abundance of the indexed populations. Flies on cattle and on traps were significantly aggregated. The degree of aggregation on traps varied with study site, whereas aggregation on faces did not vary with site.