The effects of diet quality and temperature on the development time and size of stable flies, Stomoxys calcitrans (L.), was evaluated. Both development time and size varied relative to diet quality and temperature, and their effects were additive. Diet quality and temperature made similar contributions to the variance in size whereas temperature was responsible for >97% of the variance in development time. Regression analysis predicted the shortest development time, egg to adult, to be 12.7 days at 32 °C and 70% nutrients. Egg to adult development varied curvilinearly relative to diet quality and temperature on the degree day 10 (DD₁₀) scale taking 261 DD₁₀ at 30 °C and 50% nutrients. The thermal threshold was 11.5 °C with a thermal constant of 248. Very few stable flies developed to adult on the poorest diet (12.5% nutrients) and adults emerged from fewer than 1% of the puparia at 35 °C. The heaviest pupae (15.4 mg) were produced with the 100% diet at 15 °C and adults had a higher probability of emerging successfully from heavier puparia. The length of the discal-medial cell of adult wings had a cubic relationship with puparia weight and peaked at 21 °C. Egg to pupariation survival was predicted to peak at 27 °C and 71% diet whereas puparia to adult survival peaked at 24 °C and 100% diet. Diet quality and temperature had no effect on sex ratio and the rate of development did not differ between the sexes. Female stable flies were ≈5% larger than males. Composite metrics for egg to pupariation and egg to adult fitness were developed. The optimum for puparia fitness was 29 °C and 78% diet quality and for adult fitness 25 °C and 83% diet quality. Diet accounted for 31% of the variance in pupal fitness and 24% of the variance in adult fitness whereas temperature accounted for 17% and 20%, respectively.

Substrates composed of hay residues, dung, and urine accumulate around winter hay feeding sites in cattle pastures, providing developmental habitats for stable flies. The objective of this study was to relate physiochemical and microbial properties of these substrates to the presence or absence of stable fly larvae. Properties included pH, temperature, moisture, ammonium concentration, electrical conductivity, and numbers of coliform, fecal coliform, Escherichia coli, and Enterococcus bacteria. Each physiochemical sample was classified as a function of belonging to one of the three 2-m concentric zones radiating from the feeder as well as presence or absence of larvae. In total, 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 the highest when the moisture content was 347% relative to dry weight and the average pH was 8.4. Larvae were recovered within all zones, with a nonsignificant, 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. In addition to the environmental parameters, cumulative degree day 10°C had a significant effect on the probability of observing stable fly larvae in a sample, indicating that unidentified seasonal effects also influenced immature stable fly populations.