Proximate causation of stable fly (Stomoxys calcitrans (L.)) host use : the influence of phenology and host blood suitability
Hale, Kristina Marjorie
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The biting fly, Stomoxys calcitrans (L.) (Diptera: Muscidae) has become a cosmopolitan pest of livestock, companion animals, and humans. Both males and females require daily blood meals and will opportunistically feed on many terrestrial mammals. They have rarely been seen to feed on birds, despite the presence of many potential hosts. A unique feeding behavior was documented at a wildlife refuge in northeast Montana when stable flies were seen congregating on the heads and eyes of West Nile-infected American white pelicans. The objectives of this investigation were to describe adult phenology near the pelican colony and to determine daily and lifetime fecundity when fed on cattle, horse, or chicken blood. From 2008-2010, relative adult abundance was measured by placing white Coroplast ® cards near the colony, around confinement lots, and along transects in pasture used by grazing cattle. Results showed that temporal dynamics varied by habitat type (2008: F = 7.4; df = 16, 191; P < 0.001; 2009: F = 17.7; df = 14, 270; P < 0.001) and that local dispersal occurred throughout the season. Weekly changes in abundance were explained by temperature, precipitation, and degree-days in 2008 (F = 12.2; r ² = 0.13) and 2010 (F = 13.8; r ² = 0.27) and by temperature and precipitation in 2009 (F = 164.6; r ² = 0.82). Stable flies from a laboratory-maintained colony were provided with cattle, horse, or chicken blood and daily and lifetime fecundity rates were measured through F 2 adult emergence. Flies fed chicken blood laid more eggs per day than those fed cattle (P = 0.008) or horse blood (P = 0.05), but lifetime fecundity was similar between treatments (x ² = 3.4; df = 2; P = 0.2) because of shorter oviposition periods in cohorts fed chicken blood. These results indicate that the nutritional composition of blood from these hosts does not explain the rarity of stable flies feeding on birds. Implications of host defenses as an explanation for stable fly behavior are discussed.