Seasonality and Diapause ofMusca autumnalis(Diptera: Muscidae) at its Southern Limits in North America, With Observations onHaematobia irritans(Diptera: Muscidae)

Abstract

The face fly (Musca autumnalis De Geer) and horn fly (Haematobia irritans ([L.])) were studied at the southern edge of the face fly's North American range, examining southern California geographic distribution, seasonal activity on cattle and in dung, and diapause. Face flies were common only at Pomona (34°03'N, 117°48'W). Other irrigated pastures, even those only slightly inland from Pomona, were probably too warm for face flies, due to a steep west (cooler) to east (warmer) temperature gradient. Horn flies were abundant at all sites. Adult densities on cattle, adults emerging from dung pats, and prevalence of fly-positive pats were assessed for both fly species throughout a year at Pomona. Summer adult horn fly densities of 500-2,000 flies per cow, or face fly densities of 3-10 flies per face, were common. Summer prevalence of face fly-positive pats and horn fly-positive pats was about 20-40% and 30-70%, respectively. Face fly adults diapaused from late October until late March and early April. Horn flies probably diapaused as pupae from late October or early November to early-mid March, although some emerged in winter. Experimental cohorts of October-emerging adult face flies were held in a representative overwintering site. They exhibited hypertrophied fat body and undeveloped oocytes, which are characteristics of diapause, and survived until the following spring. The dominant diapause cues in face and horn flies are probably photoperiod and temperature. Despite warm winter temperatures that would permit activity of both species, and despite relatively long winter day lengths, face flies and most horn flies still diapaused at this latitude.

Dividing the pie: differential dung pat size utilization by sympatric Haematobia irritans and Musca autumnalis

“…Horn flies can thrive in hot and sometimes dry tropics and subtropics in Latin America (Mendes & Linhares, 1999) and Africa (McLintock & Depner, 1954), whereas face flies are most abundant in the cool, northern regions of Europe, North America and Western Asia (Krafsur & Moon, 1997). Face flies in southern California are at the extreme southern edge of their North American range, and probably are limited by both low moisture and high temperature (Krafsur & Moon, 1997;Fowler et al, 2015). So face fly persistence in southern California is especially interesting.…”

“…In October 2013 and March and April 2014, additional dung cores were taken. Abundant numbers of horn flies emerge from pupal diapause a month earlier in the spring at CPP whereas far fewer overwintering face fly adults are active (Fowler et al , ). Similarly, face flies were more abundant than horn flies during the autumn (Fowler et al , ).…”

“…Abundant numbers of horn flies emerge from pupal diapause a month earlier in the spring at CPP whereas far fewer overwintering face fly adults are active (Fowler et al , ). Similarly, face flies were more abundant than horn flies during the autumn (Fowler et al , ). These marked seasonal windows in which one fly species' immatures were abundant in dung pats, whereas the alternate fly species' immatures were rare or absent.…”

“…Irrigated beef cattle pastures at California Polytechnic State University, Pomona (CPP) (34°03′N, 117°48′W, 225 m elevation) supported both face flies and horn flies (Soto et al , ; Fowler et al , ). Two beef cattle herds ranging from 12 to 20 adult cows and calves were rotated among multiple pastures.…”

Research Progress on Diapause in Flies (Diptera)

“…Diapause in some species of flies is subject to both photoperiod and temperature; for example, the dominant diapause cues of M. autumnalis and H. irritans are probably both photoperiod and temperature [40]. The critical day length for Aphidoletes aphidimyza diapause induction is determined to be 12.7 h at 20°C.…”