The biting midges, “no-see-ums,” or punkies belong to the family Ceratopogonidae. The most common biting midges areCulicoidesspp. They are associated with aquatic or semiaquatic habitats, eg, mud or moist soil around streams, ponds, and marshes. Biting midges are tiny gnats (1–3 mm long) and, like black flies, inflict painful bites and suck the blood of their hosts, both humans and production animals.
Pathology of Biting Midges
Culicoides spp are aggressive blood-feeding insects and vicious biters that can cause intense irritation, stress, and production losses in a wide range of domestic and wild animals. Heavy biting activity leads to restlessness, altered behavior, decreased grazing or feeding efficiency, and decreased productivity in livestock.
Biting midges fly only in the warm months of the year and are most active before and during dusk. Their bites can induce hypersensitivity reactions in susceptible animals.
Feeding site preferences vary between Culicoides spp and host species, with bites commonly occurring on areas of thin skin, including the ventral abdomen, flanks, udder, ears, neck, tail region, and other sparsely haired areas.
Biting midges feed often on the mane, tail, and belly of horses. Horses are particularly prone to developing insect-bite hypersensitivity, characterized by intense pruritus; scratching and rubbing these areas (self-trauma) causes alopecia, excoriations, and crusting and thickening of the skin, most commonly affecting the mane, tail, ventral abdomen, and withers. This condition has several names, including culicoid hypersensitivity in Canada, Queensland itch in Australia, kasen in Japan, sweat itch, and sweet itch. Because it often occurs during the warmer months of the year, it is also referred to as summer dermatitis. (See images of .)
Horse with sweet itch, a common seasonal allergic skin response to the saliva of biting midges (Culicoides species). Sweet itch A) between the horse's eyes; B) around the withers; C) near the tail area; and D) on the tail.
Courtesy of Dr. Andrea Harvey.
Similar hypersensitivity syndromes have been reported in other species, including cattle, sheep, dogs, and wild animals; however, they are generally less extensively documented than in horses.
Beyond their direct effects, Culicoides spp are among the most important arthropod vectors of pathogens affecting animal health worldwide. They are the principal vectors of bluetongue virus in cattle, sheep, goats, and wild ruminants and are responsible for transmitting other economically important arboviruses, including hemorrhagic disease virus, African horse sickness virus, and Schmallenberg virus. The veterinary importance of Culicoides spp extends beyond nuisance and allergic dermatitis because of their central role in the epidemiology of major transboundary animal diseases (TADs).
In addition to transmitting viruses, some Culicoides spp serve as the intermediate hosts of parasitic nematodes. In horses, biting midges transmit Onchocerca cervicalis, with microfilariae of this nematode found in the skin of horses. Equine onchocerciasis is a nonseasonal dermatosis that is similar to sweet itch but usually is less pruritic and affects the head, neck, and belly.
Diagnosis of Biting Midges
Like black flies and sand flies, biting midges are usually collected from the environment rather then from affected animals. Diagnosis is therefore based primarily on clinical presentation, seasonality, geographical distribution, and collection of insects from the affected premises. Identification of biting fly species can be challenging because multiple groups of biting fly species can be simultaneously present.
Adult Culicoides are considerably smaller then most black flies and often referred to as no-see-ums, as noted above, because of their small size (see ). Unlike black flies, which possess the broad, clear wings with prominent venation and characteristic hump-backed appearance, Culicoides typically have patterned or densely mottled wings that are used for species identification, whereas sand flies can be distinguished by their densely hairy wings, which are held in a characteristic V shape above the body when resting.
Culicoides newsteadi, a tiny biting midge species found in Europe and North Africa.
Courtesy of ABOL/HP Fuehrer Vetmeduni Vienna
Identification of biting midge species is complex and best left to an entomologist.
Treatment and Control of Biting Midges
Limit exposure, particularly at dusk and dawn
Protect by shelter or blanketing
Apply insecticides and repellents
Control of Culicoides spp remains challenging. Unlike black flies (Simulium spp), whose larval stages are often concentrated in flowing water habitats that can be targeted with larvicides, or sand flies (Phlebotominae), whose populations can be decreased through environmental modification and residual insecticide treatments, biting midges typically develop in a wide range of moist organic substrates: mud, manure-enriched soil, irrigated pastures, pond margins, and other natural habitats. These breeding sites are often extensive, dispersed, and difficult to identify, making large-scale larval control impractical in most situations. As a result, management of Culicoides is generally directed at decreasing host exposure rather than attempting to suppress population.
Larvae can be attacked in their breeding grounds. Extension entomology personnel should be contacted to identify local larval breeding grounds and provide advice on the latest approved recommendations.
Because Culicoides spp are poor fliers, increasing air movement with an electric fan can decrease host-seeking and feeding activity and may be used in stables, kennels, animal housing, and other premises affected by biting midges.
Control of major bluetongue virus vectors—including C sonorensis in North America, C imicola in Africa and the Mediterranean region, and C brevitarsis in Australia—is challenging because each species has different breeding habitats and ecological environments, limiting the effectiveness of universal control strategies. Therefore, effectiveness of insecticides, repellents, residual treatments, fogging, and environmental management varies considerably among Culicoides species, geographical regions, and husbandry systems. No single control strategy can be generally applied, and integrated approaches are generally necessary.
For More Information
Bluetongue. USDA Animal and Plant Health Inspection Service.
Bluetongue. WOAH.
Also see pet owner content regarding flies and mosquitoes of dogs, cats, and horses.
