Chapter 16 - Horse Flies and Deer Flies (Tabanidae)

Abstract

Tabanidae is among the most species-rich of all blood-feeding Diptera families. These large flies, 10 to 30 mm in length, impact people and animals via direct effects (nuisance, reduced weight gains in animals) and disease agent transmission. Species typically have one generation per year and distinct seasonal activity periods, laying egg masses on substrates such as emergent pond edge vegetation. Females of key pest genera such as Tabanus or Hybomitra (horse flies) or Chrysops (deer flies) usually require blood for oogenesis, but some haematophagous species are autogenous in the first gonotrophic cycle and others do not blood-feed at all. Immatures usually inhabit moist, semiaquatic substrates; some are terrestrial or live in rivers or streams. Larvae are predaceous on macroinvertebrates and pupate above waterline. Tabanids are mostly day-biters and are excellent mechanical transmitters of disease agents, due to their large size, painful bites, and frequently interrupted blood meals. Key mechanically-transmitted agents include equine infectious anemia virus, Trypanosoma evansi (surra), and Franciscella tularensis (rabbit fever or deer fly fever). Agents biologically-transmitted by tabanids are less common but include the human filarial nematode Loa loa (African eyeworm) and Elaeophora schneideri (arterial worm of elk or deer). Horse and deer flies are monitored and may sometimes be locally controlled using traps with visual cues such as dark colors (black, blue) and chemical cues such as carbon dioxide, 1-octen-3-ol, or animal urine. Insecticides or repellents applied to people or animals may offer short-term relief, but generally are less effective against tabanids than other biting Diptera.