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

Abstract

Horn flies [Haematobia irritans (Diptera: Muscidae) (L.)] and face flies [Musca autumnalis (Diptera: Muscidae) De Geer] use the same larval resource, but their interactions are poorly studied. Dung pats (n = 350) were core sampled in the summers of 2012 and 2013 from irrigated pastures in Pomona, California, U.S.A. (34°03'N, 117°48'W) and held for face fly and horn fly emergence. Surface areas and estimated weights were recorded for each whole pat. Almost half (42.0%) of the pat cores yielded neither fly, 29.7% yielded horn flies only, 12.9% yielded face flies only and 15.4% yielded both flies. Of the fly-positive pats, surface area and mass were larger for face fly-occupied pats, whereas horn fly-occupied pats were smaller. Pats shared by the two species were intermediate. Horn flies per positive core were unaffected by the absence/presence of face flies, but half as many face flies emerged when pats were co-inhabited by horn flies. Face flies inhabited larger pats, which might better resist heating and drying, to which they are susceptible; horn flies inhabited a broad pat size range. Horn fly tolerance of lower dung moisture probably allows horn flies to colonize and survive in a wide range of pats in dry areas like southern California.

Pasture dragging fails to reliably suppress the emergence of horn flies (Haematobia irritans) and face flies (Musca autumnalis) from dung pats in aMid‐AtlanticNorth American climate

“…Horn flies were not reliably suppressed by the mechanical drag in 2018 nor the manual spreader in 2020. Given the large variation in natural populations of horn flies per pat seen here and in other studies (e.g., see Fowler & Mullens, 2016), it is possible that a small but real suppressive effect of pasture dragging occurs, at least under some conditions, but was not detected in our experiment. This notion seems somewhat plausible if June 2018 (Figure 2a) and July 2020 (Figure 3a) are considered in isolation from the other dates.…”