Environmental Parameters Associated with Stable Fly (Diptera: Muscidae) Development at Hay Bale Feeders.

Substrates composed of hay residues, dung, and urine accumulate around winter hay feeding sites in cattle pastures providing developmental habitat for stable flies. The objective of this study was to relate physiochemical and microbial properties of this substrate to the presence or absence of developing stable fly larvae. Properties included pH, temperature, moisture, ammonium concentration, electrical conductivity, and numbers of coliform, fecal coliform, E. coli, and Enterococcus bacteria. Each physiochemical sample was classified as a function of belonging to one of three 2 m concentric zones radiating from the feeder as well as presence or absence of larvae. A total of 538 samples were collected from 13 sites during 2005 – 2011. Stable fly larvae were most likely to be found in moist, slightly alkaline substrates with high levels of ammonium and low temperature. The probability of larvae being present in a sample was highest when the moisture content was 47% and the average pH was 8.4. Larvae were recovered within all zones, with a non-significant, but slightly higher percentage of samples containing larvae taken 2 – 4 m from the center. All methods used to enumerate bacteria, except total coliform, indicated decreasing concentrations in hay bale residue throughout the summer. After environmental parameters were used to account for larval presence, analyses indicated that cumulative DD₁₀ was also significant.  This indicates that in addition to substrate quality, an unexplained seasonal effect may also influence stable fly development.