Tabanids

Members of the family Tabanidae are nuisance pests for livestock and people, due to their painful and irritating bite, persistent biting behaviour, and blood ingestion (Baldacchino et al., 2014). They can furthermore also be bothersome to wildlife species (Baldacchino et al., 2013). Besides causing economic losses based on direct effects, they are important vectors for a number of disease agents (viruses, bacteria, protozoa, filarial nematodes), including Trypanosoma evansi, which can affect camels and equids causing Surra, but which can also cause trypanosomosis in form of a fatal disease in dogs (Echeverria et al., 2019) and which has been reported in cats (e.g., Tarello, 2005; Misra et al., 2016). The transmission of this protozoan occurs mechanically by tabanid species of the genera Tabanus, Haematopota and Chrysops.

Photograph of adult tabanid1
  • 1. By courtesy of D. Bowman, University of Cornell, Ithaca, NY, USA.

General

Taxonomy

The family Tabanidae comprises more than 4,600 species belonging to 170 genera and is divided into six subfamilies: Chrysopsinae, Tabaninae, Adersiniiae, Pangoniinae, Rhagioniinae and Therevinae (Bánki et al., 2021). The first two subfamilies contain most of the economically important tabanids (Mullens, 2019). They are commonly referred to as horse flies, deer flies, or clegs. Tabanids in the subfamily Chrysopinae are called deer flies, with nearly all being members of the genus Chrysops. The term horse fly is generally applied to most of the Tabaninae species, except the tribe Haematopotini. The term cleg is used for Haematopota spp. within the subfamily Tabaninae.

 

Classification of tabanids

Phylum: Arthropoda
Class: Insecta
Order: Diptera (i.e. two-winged insects)
Suborder: Brachycera
Family: Tabanidae
Subfamily: Chrysopsinae, Tabaninae, Adersiniiae, Pangoniinae, Rhagioniinae, Therevinae
Genus: e.g., Chrysops, Tabanus

 

Distribution

Tabanids are present on every continent except Antarctica (Mullens, 2019). Large seasonal populations of some species occur as far as 60° N latitude, but they disappear above tree line. Diversity within the family is greatest in the tropics, but moist temperate regions have a rich fauna as well (Mullens, 2019).

Epidemiology

Tabanids possess a wide spectrum of hosts, including wildlife, livestock and men. They are among the most free-living adult flies which play a role as livestock pests as well as vectors of various disease pathogens. A single blood meal is used as a source of energy for egg production (100-1,000 eggs per meal) in tabanids, and females of certain species can additionally oviposit before a first blood meal is obtained (autogenous). Therefore, the maintenance of annual tabanid populations requires successful oviposition by only 2% of females. This and the life cycle factors that (i) female adults spend only few minutes feeding on a host to obtain enough blood to produce eggs, (ii) tabanids can feed on domestic hosts, but also on wild hosts which are sufficient blood sources to maintain populations, and (iii) tabanids lay their eggs in a wide variety of sites and the larvae are ubiquitous throughout the environment (Foil and Hogsette, 1994), makes effective reduction of tabanid population a challenge. In most cases, control of tabanids has to be based on protective measures against adults rather than larvae (Baldacchino et al., 2014).

As mentioned before, tabanids may act as vectors of disease pathogens via mechanical transmission. Here, overall, they have all the characteristics of good mechanical vectors, namely by frequently engaging in interrupted feeding, by being highly mobile and by endowing with large mouthparts (Baldacchino et al., 2014).

Some pathogens and parasites are also transmitted biologically by tabanids, in which cases the disease agent replicates and/or develops within the fly for a period of time prior to transmission (e.g., the filarial nematode Loa loa) (Mullens, 2019).

Morphology

Tabanid adults are stout-bodied flies. They can generally be distinguished as horse flies or deer flies based on several morphological characteristics (see Table 1). The antennae are prominent and extent anteriorly. In general, they possess a fairly large size, striking appearance and mainly diurnal habits. The eyes of many species are brilliantly patterned with shades of green, yellow, orange, and violet. They often consist of large ommatidial facets dorsally and smaller facets ventrally. The antennae are divided into three parts and are of major importance for classification (Baldacchino et al., 2014). Tabanids are pool feeders (Mullens, 2019), in contrast e.g. to vessel feeding in mosquitoes. For further details on morphology see e.g., Mullens (2019) and Baldacchino et al. (2014). Tabanids are fast flyers with high dispersal ability, e.g. 1-2 km daily (Cooksey and Wright, 1987; Kostantinov, 1993). Wings have a constant venation within the Tabanidae (Baldacchino et al., 2014). One of the main characteristics of tabanids is the variety and diversity of bold colours and patterns on different body parts such as eyes, wings and abdomen (McKeever and French, 1997). These distinctive colours and patterns are useful for identification, whereas their function remains so far unclear (Baldacchino et al., 2014).

The developmental cycle includes the following stages: Egg, 1-3 mm long, which is deposited in masses; larva (predaceous and cannibalistic), performing 6-13 larval molts with larvae overwintering; a pupal stage and the adult stage.

Morphological characteristics used to differentiate adult horse and deer flies (Mullens, 2019)

Characteristic Horse flies (e.g., Tabanus) Deer flies (e.g., Chrysops)
Body length 10-30 mm 6-11 mm
Antennae Short, base of flagellum greatly enlarged Long, base of flagellum not greatly enlarged
Ocelli Vestigiial or lacking Present
Wings Clear, uniformly cloudy or spotted Distinctly banded
Apical spurs on hind tibiae Lacking Present

 

Feeding

Males feed on nectar, honeydew and other liquids, and females feed on these substances and on blood. Females of most species must obtain a blood meal prior to the development of each batch of eggs, thus seeking a bloodmeal after mating. However, some species lay one batch of eggs before they seek an animal host (autogeny) or are non-hematophageous. For more details see also Baldacchino et al. (2014) and Foil and Hoogsette (1994).

The blood-meal size of a female tabanid ranges from 20 µL for smaller species to up to 600 µL for larger species (Hollander and Wright, 1980).

Regarding the transmission of pathogens, tabanids more commonly transmit mechanically. This is as well the case for Trypanosoma evansi, in contrast to other insects assisting in the transmission of Trypanosoma species.

Activity Dynamics

In most areas, tabanid activity is highly seasonal; in temperate climates high activity occurs in the warmer months, typically summer (Altunsoy and Kilic, 2012; Baldacchino et al., 2013; McElligott and Lewis, 1998). The seasonal flight periods of most of the temperate species vary little from year to year. In the tropics, activity usually peaks during the rainy season (Barros, 2001; Okiwelu, 1975). However, these patterns may vary, even within a given species (Baldacchino et al., 2014).

Tabanids are strong fliers and readily disperse several kilometres in short-term flights. But it was suggested, based on mark-release-recapture studies, that local populations tend to remain in a given area, with dispersal occurring in a series of short flights.

Activity is generally diurnal either in a unimodal peak or in bimodal peaks (Baldacchino et al., 2013; Cilek and Schreiber, 1996; Harley, 1965; Oliveira et al., 2007). This pattern may vary among seasons in a given species. Daily activity patterns are related to meteorological variables such as temperature, relative humidity, wind speed or atmospheric pressure, and each species responds differently (Amano, 1985; Van Hennekeler et al., 2011). In temperate climates, tabanid activity is low at cool temperatures in the morning, resulting in an activity peak typically at noon or in the early afternoon (Baldacchino et al., 2013; Ganeva, 1999; McElligott and Galloway, 1991). In contrast, activity periods in tropical areas may vary across seasons. In high rainfall areas such as French Guiana, most of the tabanid species are active early in the morning and late in the afternoon, because the temperature at noon is high (Raymond, 1989).

Host Spectrum

Females, particularly of the Tabaninae, attack mainly livestock, especially large mammals (cattle, horses, deer). Chrysops and Haematopota have a wider variety of hosts including people (Baldacchino et al., 2014). Females are attracted to large, dark, moving objects and to CO2 (Strother, 1999).

Cats and dogs can also be attacked as feeding source. Some species of deer flies were also recorded to feed on ravens, crows, ducks and robins. Many tabanids are selective in attacking specific body regions of their hosts, regardless of colour.

Life Cycle

Tabanids are holometabolous insects, meaning that they go through the following life cycle stages: egg, larva, pupa and adult. Although the life histories of the members of this large family of flies differ, they can be generalized as illustrated below.

Egg

Eggs are usually laid in large, layered clusters of 100-1000 on vegetation or other objects overlying water or moist soil (Strother, 1999). Embryogenesis requires two to 21 days, depending on species and on climatic conditions. Egg hatch occurs more quickly when relative humidity and temperatures are high (Chvála et al., 1972; Mullens, 2002).

The subsequent larvae hatch from the eggs and drop to the water or soil below where they become predators of other invertebrates or small vertebrates (Strother, 1999).

Larva

The larvae of Tabanids are white to tan, with a slender, cylindrical body that is slightly tapered at the head (Strother, 1999). They are found in a wide variety of biotopes with a diversity of moist conditions. Larvae of most tabanids are found in specific habitats, but their adaptability and hardiness also enable them to develop in other habitats (Baldacchino et al., 2014). They can be separated in three morpho-ecological groups, depending on their habitat: (i) rivulets (rivers) and streams, (ii) slow moving or stagnant water bodies, or littoral areas (banks), (iii) drier soil, usually far from water bodies (Andreeva, 1982; Andreeva et al., 2009). Thus, they are aquatic, semi-aquatic, or terrestrial. After hatching, they become predators of other invertebrates or small vertebrates (Strother, 1999). They feed on worms and larvae of other Diptera, and they are also cannibalistic. They can survive a long time without feeding and can hibernate several times, two or three times in northern regions. Most temperate species have one generation per year, but some tropical species have two or three generations per year. Large temperate species may spend two or three years as larvae (Baldacchino et al., 2014). Once the larva is fully developed it moves into drier soil to pupate (Strother 1999). The number of larval stages ranges from 6 to 13.

Pupa

Pupation occurs in dry places and lasts one to 3 weeks (Baldacchino et al., 2014). Finally, the adult flies emerge from the soil.

Adult

Male adults emerge before female adults. Shortly after adult emergence, mating occurs. Tabanid mating occurs in flight, especially in the morning (Wilkerson et al., 1985). After mating, females lay in wait in vegetation until a host for a blood meal wanders into range. Females are attracted to large, dark, moving objects and to CO2. Most females seek a blood meal after mating except for non-hematophagous females (e.g., Pangonius sp.), and autogenous hematophagous females (e.g., Tabanus nigrovittatus), which do not need a blood meal for the first oviposition. Females, particularly the Tabaninae, attack mainly livestock, especially large mammals (cattle, horses, deer). Chrysops and Haematopota have a wider variety of hosts including people. Oviposition occurs three to 11 days after feeding.

Adults of both sexes obtain also sugars from nectar and other natural plant sugar deposits which provide energy for body maintenance, flight, and mating.

The longevity of adults is about two or 3 weeks; this is very short relative to the larval stage (Chvála et al., 1972). Life cycles require from two months to two years, depending on the species and the geographical location. In most regions, adults of most species are only present for approximately one month, but a succession of species is often seen. The result is that livestock may be attacked by one or more species of Tabanidae throughout all or most of the warm months of the year (Foil and Hoogsette, 1994).

For further detailed information see also Baldacchino et al. (2014), Foil and Hoogsette (1994), Mullens (2019) and Strother (1991)

Prevention

Tabanids are nuisance pests of people and livestock. They cause extreme annoyance and blood loss due to feeding and oozing (Foil and Hogsette, 1994). Tabanids have a painful bite, based on the large size of their mouthparts and the damaging feeding mechanism, which in turn induces host defensive movements, leading to interrupted feeding. Owing to their painful, persistent biting behaviour they further cause reductions in weight gain, milk yield and feed-utilisation efficiencies. Tabanids can retain a large amount of blood (7–15 nL) in their mouthparts, especially when compared to Stomoxys (0.4 nL) or mosquitoes (0.001–0.0001 nL) (Foil and Gorham, 2000), which again makes them 20-20,000 times more efficient mechanical vectors than other biting insects (Baldacchino et al., 2014). Thus, apart from being serious pests, tabanids are very capable vectors of a large number of viruses, bacteria/rickettsia, filarial nematodes and protozoa, usually by mechanical transmission. For a detailed listing on transmitted pathogens see Baldacchino et al. (2014) and Mullens (2019).

Tabanids are considered to be the most challenging livestock pests to control, due to a number of factors, mostly associated with their life cycle. These factors are as follows: (i) female adults spend only few minutes feeding on a host to obtain enough blood to produce eggs, (ii) they can feed on domestic hosts, but also on wild hosts which are sufficient blood sources to maintain populations, and (iii) they lay their eggs in a wide variety of sites and the larvae are ubiquitous throughout the environment. An overall constraint is also the biological and ecological diversity of tabanids; this severely constrains any single approach (Baldacchino et al., 2014). The tendency to generalize about a family of over 4,600 species and 170 genera probably is the most important factor. Due to the complex life cycle which is partly independent of livestock, integrated control strategies are required to reduce the impact of these pests (Foil and Hoogsette, 1994).

Control of tabanids can be approached differently, including chemical, cultural, mechanical and biological control. For detailed information see also Foil and Hoogsette (1994).

A number of different traps with a variety of modifications has been developed and is used for control or epidemiological studies. Efficacy may be different and extrapolation from the trap catches to the burden of life stock might be limited. Traps using sensory cues such as sound, odour, colour, intensity (darkness/brightness), movement, and light polarization have been designed to attract the targeted insects (Egri et al., 2012; Horváth et al., 2008; Kriska et al., 2009; Takken and Knols, 2010). For more details on surveillance systems see Foil and Hoogsette (1994), Baldacchino et al. (2014) and Mullens (2019). Regardless of the choice of surveillance method, several factors should be considered. Tabanid flight activity and host-seeking behaviour is influenced by daily rhythms, weather and location of vegetation; the influence of these factors differs between species.

Besides different traps, insecticides, repellents, pasture and grazing management, as well as water and animal management have been tested and used for surveillance respectively control. Detailed information on the different approaches can be found in Foil and Hoogsette (1994), Baldacchino et al. (2014) and Mullens (2019).

Regarding dogs and cats, which can potentially be affected by the transmission of Trypanosoma evansi, no special data regarding control or prevention methods is published.

References

Introduction

Baldacchino F, Desquesnes M, Mihok S, et al.: Tabanids: neglected subjects of research, but important vectors of disease agents! Infect Genet Evol. 2014, 28, 596-615

Baldacchino F, Gardes L, De Stordeur E, et al.: Blood-feeding patterns of horse flies in the French Pyrenees. Vet Parasitol. 2013, 199, 283-8

Echeverria JT, Soares RL, Crepaldi BA, et al.: Clinical and therapeutic aspects of an outbreak of canine trypanosomiasis. Rev Bras Parasitol Vet. 2019, 28, 320-4

Misra KK, Roy S, Choudhury A: Biology of Trypanosoma (Trypanozoon) evansi in experimental heterologous mammalian hosts. J Parasit Dis. 2016, 40, 1047-61

Tarello W: Trypanosoma evansi infection in three cats. Revue Méd Vét. 2005, 156, 133-4

 

General

Baldacchino F, Desquesnes M, Mihok S, et al.: Tabanids: neglected subjects of research, but important vectors of disease agents! Infect Genet Evol. 2014, 28, 596-615

Bánki O, Roskov Y, Vandepitte L, et al.: Catalogue of Life Checklist (Annual Checklist 2021). 2021, Catalogue of Life, https://www.catalogueoflife.org/

Foil LD, Hogsette JA: Biology and control of tabanids, stable flies and horn flies. Rev Sci Tech. 1994, 13, 1125-58

Mullens BA: Horse flies and deer flies (Tabanidae). In: Mullen GA, Durden LA (eds.): Medical and Veterinary Entomology. 2019, 3rd edn., Academic Press, Elsevier Inc., London, San Diego, pp 327-43

 

Morphology

Baldacchino F, Desquesnes M, Mihok S, et al.: Tabanids: neglected subjects of research, but important vectors of disease agents! Infect Genet Evol. 2014, 28, 596-615

Cooksey LM, Wright RE: Flight range and dispersal activity of the hostseeking horse fly, Tabanus abactor (Diptera, Tabanidae), in north central Oklahoma. Environ Entomol. 1987, 16, 211-7

Konstantinov SA: The attack distance and the range and nature of the daily flight dispersion of horseflies in the genus Hybomitra (Diptera: Tabanidae). Parazitologiia. 1993, 27, 419-26

McKeever S, French FE: Fascinating, beautiful blood feeders: deer flies and horse flies, the Tabanidae. Am Entomol. 1997, 43, 217-26

Mullens BA: Horse flies and deer flies (Tabanidae). In: Mullen GA, Durden LA (eds.): Medical and Veterinary Entomology. 2019, 3rd edn., Academic Press, Elsevier Inc., London, San Diego, pp 327-43

 

Feeding

Altunsoy F, Kilic AY: Seasonal abundance of horse fly (Diptera: Tabanidae) in Western Anatolia. J Entomol Res Soc. 2012, 14, 95-105

Amano K: Statistical analyses of the influence of meteorological factors on flight activity of female tabanids. Kontyu (Tokyo). 1985, 53, 161-72

Baldacchino F, Desquesnes M, Mihok S, et al.: Tabanids: neglected subjects of research, but important vectors of disease agents! Infect Genet Evol. 2014, 28, 596-615

Baldacchino F, Porciani A, Bernard C, et al.: Spatial and temporal distribution of Tabanidae in the Pyrenees Mountains: influence of altitude and landscape structure. Bull Entomol Res. 2013, 104, 1-11

Barros AM: Seasonality and relative abundance of Tabanidae (Diptera) captured on horses in the Pantanal, Brazil. Mem Inst Oswaldo Cruz. 2001, 96, 917-23

Cilek JE, Schreiber ET: Diel host-seeking activity of Chrysops celatus (Diptera: Tabanidae) in northwest Florida. Fla Entomol. 1996, 79, 520-5

Foil LD, Hogsette JA: Biology and control of tabanids, stable flies and horn flies. Rev Sci Tech. 1994, 13, 1125-58

Ganeva D: Daily activity of Tabanus bromius L., Tabanus tergestinus Egg. and Haematopota pluvialis L. (Tabanidae, Diptera) in the Stara Zagora district. Period Biol. 1999, 101, 215-20

Harley JMB: Seasonal abundance and diurnal variations in activity of some Stomoxys and Tabanidae in Uganda. Bull Entomol Res. 1965, 56, 319-32

Hollander AL, Wright RE: Impact of tabanids (Diptera: Tabanidae) on cattle: blood meal size and preferred feeding sites. J Econ Entomol. 1980, 73, 431-3

McElligott PEK, Galloway TD: Daily activity patterns of horse flies (Diptera, Tabanidae, Hybomitra spp.) in northern and southern Manitoba. Can Entomol. 1991, 123, 371-8

McElligott PEK, Lewis DJ: Seasonal changes in abundance and gonotrophic age of host-seeking Tabanidae (Diptera) from a subarctic Labrador peatland. J Med Entomol. 1998, 35, 763-70

Okiwelu SN: Seasonal distribution and variations in diurnal activity of Tabanidae in the republic of Zambia. Mosq News. 1975, 35, 551-4

Oliveira AF, Ferreira RLM, Rafael JA: Seasonality and diurnal activity of Tabanidae (Diptera: Insecta) of canopy in the Adolpho Ducke Forested Reserve, Manaus, Amazonas State, Brazil. Neotrop Entomol. 2007, 36, 790-7

Raymond HL: Distribution temporelle des principales especes de taons (Diptera. Tabanidae) nuisibles au betail en Guyane Francaise. Ann Soc Entomol Fr. 1989, 25, 289-94

Strother S: Genus Tabanus. Tabanids (horseflies). What is this insect and how does it affect man? Dermatol Online J. 1999, 5, 6

Van Hennekeler K, Jones RE, Skerratt LF, et al.: Meteorological effects on the daily activity patterns of tabanid biting flies in northern Queensland, Australia. Med Vet Entomol. 2011, 25, 17-24

 

Life Cycle

Andreeva VR: On ecologo-morphological typing of tabanid larvae (Diptera, Tabanidae). Entomol Rev. 1982, 64, 49-54

Andreeva VR, Kilic AY, Altunsoy F: New contribution to information about tabanidae (Diptera) adult and larvae from West Anatolia. J Entomol Res Soc. 2009, 11, 19-30

Baldacchino F, Desquesnes M, Mihok S, et al.: Tabanids: neglected subjects of research, but important vectors of disease agents! Infect Genet Evol. 2014, 28, 596-615

Chvála M, Lyneborg L, Moucha J: The horse flies of Europe (Diptera, Tabanidae). 1972, Entomological Society of Copenhagen, Copenhagen, p 498

Foil LD, Hogsette JA: Biology and control of tabanids, stable flies and horn flies. Rev Sci Tech. 1994, 13, 1125-58

Mullens BA: Horse flies and deer flies (Tabanidae). In: Mullen G, Durden L (eds.): Medical and Veterinary Entomology. 2002, Academic Press, Elsevier Inc., San Diego, pp 263–277

Mullens BA: Horse flies and deer flies (Tabanidae). In: Mullen GA, Durden LA (eds.): Medical and Veterinary Entomology. 2019, 3rd edn., Academic Press, Elsevier Inc., London, San Diego, pp 327-43

Strother S: Genus Tabanus. Tabanids (horseflies). What is this insect and how does it affect man? Dermatol Online J. 1999, 5, 6

Wilkerson RC, Butler JF, Pechuman LL: Swarming, hovering, and mating behavior of male horse flies and deer flies (Diptera: Tabanidae). Myia. 1985, 3, 515-46

 

Prevention

Baldacchino F, Desquesnes M, Mihok S, et al.: Tabanids: neglected subjects of research, but important vectors of disease agents! Infect Genet Evol. 2014, 28, 596-615

Egri A, Blaho M, Kriska G, et al.: Polarotactic tabanids find striped patterns with brightness and/or polarization modulation least attractive: an advantage of zebra stripes. J Exp Biol. 2012, 215, 736-45

Foil LD, Hogsette JA: Biology and control of tabanids, stable flies and horn flies. Rev Sci Tech. 1994, 13, 1125-58

Horváth G, Majer J, Horvath L, et al.: Ventral polarization vision in tabanids: horseflies and deerflies (Diptera: Tabanidae) are attracted to horizontally polarized light. Naturwissenschaften. 2008, 95, 1093-100

Kriska G, Bernath B, Farkas R, et al.: Degrees of polarization of reflected light eliciting polarotaxis in dragonflies (Odonata), mayflies (Ephemeroptera) and tabanid flies (Tabanidae). J Insect Physiol. 2009, 55, 1167-73

Mullens BA: Horse flies and deer flies (Tabanidae). In: Mullen GA, Durden LA (eds.): Medical and Veterinary Entomology. 2019, 3rd edn., Academic Press, Elsevier Inc., London, San Diego, pp 327-43

Takken W, Knols BGJ: Olfaction in vector-host interactions. Vol. 2, 2010, Wageningen Acadaemic Publishers, Wageningen, The Netherlands, p 437

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