Biting Midges

Culicoides spp are vicious biters and can cause intense irritation and annoyance. In large numbers, they can cause livestock to be nervous and interrupt their feeding patterns. These gnats tend to feed on the dorsal or ventral areas of the host; feeding site preference depends on the species of biting gnat. They fly only in the warm months of the year and are most active before and during dusk. They feed often on the mane, tail, and belly of horses. Horses often become allergic to the bites, scratching and rubbing these areas, causing alopecia, excoriations, and thickening of the skin. This condition has several names, including culicoid hypersensitivity in Canada, Queensland itch in Australia, Kasen in Japan, sweat itch, and sweet itch. Because it is often seen during the warmer months of the year, it is also referred to as summer dermatitis. These flies also serve as the intermediate host for Onchocerca cervicalis; the microfilariae of this nematode are found in the skin of horses. Onchocerciasis (see Onchocerciasis) is a nonseasonal dermatosis that is similar to sweet itch but usually is less pruritic and affects the head, neck, and belly. These flies also transmit the bluetongue virus (see Bluetongue) in sheep and cattle.

Like black flies and sand flies, biting midges are most often collected in the field and not found on the animals. In contrast to the clear, heavily veined wings of black flies, the wings of Culicoides spp are mottled. Identification is probably best left to an entomologist.

Larvae may be attacked in their breeding grounds. Extension entomology personnel should be contacted for the latest approved recommendations.

Bio Kill Stable Spray™, a modified permethrin, is approved for the spraying of stables and horseboxes to aid in the control of biting midges. A backpack or handheld bulk pesticide spray pack, turbo-blower, or fogger should be used. A fine spray should be produced under pressure, in the amount of 500–750 mL per stable (stable size: 3 m × 3.5 m to 4 m × 4 m). All surfaces in the stable should be sprayed. A reapplication 7–10 days later is needed. Thereafter, application every 3–4 wk should provide ample product buildup on the walls.

Because Culicoides spp are poor flyers, an electric fan may be used in the stable to create air movement around the horses. Fly repellent ear tags attached to the horse’s mane and tail (not approved in the USA); pyrethrum synergized with piperonyl butoxide, applied weekly; butoxypolypropylene glycol 800, applied daily; stable blankets; and fine screens on stable doors and windows have been used with mixed success. Topical insecticides such as pyrethrins (eg, cypermethrin or cyfluthrin), especially in pour-on formulations, may also be used to control these adult pests in large animals.