PB1478
HORSE PEST MANAGEMENT

Gene Burgess, Professor, Entomology and Plant Pathology

Insect and related parasites cause direct and indirect damage to horses. They feed on the horses; cause irritation; spread diseases; and cause digestive upsets, poor condition and retarded growth. Therefore, strong parasite control programs are needed. Many different flies are pests of horses. Basically, they may be divided into three groups by their feeding habits. Sponging mouthparts, found on house flies and face flies, are used to sponge or sop up liquid foods. Stable flies, horn flies, horse flies and mosquitoes use piercing mouthparts to pierce the host animal's skin so that they may feed on blood. Some flies, such as bots and cattle grubs, have no mouthparts as adults.

HORSE BOTS
There are three bot flies that attack horses. The common bot fly, Gasterophilus
intestinalis, lays his yellow-white eggs on the hairs of the horses' forelegs, chest, neck, belly and sometimes on the hind legs and flanks. These eggs incubate one to two weeks and hatch only if licked or eaten. The moisture, warmth and friction from the licking stimulates larval hatch. The young bot larvae then migrate to the mouth of the horse. They burrow into the front of the tongue and three to four weeks later emerge out the rear of the tongue before migrating and attaching to the stomach wall.

The female throat bot fly, Gasterophilus nasalis, lays her eggs on the hairs under the jaw and throat. Incubation takes four to six days and larvae hatch without stimulation. These larvae infest the gum margins around the cheek teeth for one month before migrating to the stomach, pylorus and duodenum. Large numbers of larvae in the gums may cause pus pockets and mouth irritation.

The female nose bot fly, Gasterophilus hemorrhoidalis, deposits black eggs on the hairs of the lips. The larvae hatch in two to four days. These larvae penetrate the inner lip membranes in front of the incisors and after five to six weeks also migrate and attach themselves to the stomach walls.

When the bot larvae are mature, they detach themselves, change into the non-feeding
pre-pupal stage as they move through the intestines and pass out with the droppings. These pre-pupae burrow into the ground where they remain one to two months. Adult flies emerge during warm summer months. The life cycle from egg to adult fly takes one year. Stomach bots cause gastrointestinal disturbances. Occasionally, they become so
numerous that they mechanically block the stomach outlet, resulting in colic. The blockage may also cause rupture of the stomach wall and death. This seldom occurs.

Bots may be controlled by several methods. Larvae can be induced to hatch by
sponging with warm (104 to 118o F) water. Sponging horses on cool days (below 60o F) will assure that larvae quickly die of exposure. Warm water may be applied with an insecticide if treatment is done on a warm day. Treating the body areas, where bot flies glue their eggs, with insecticide wipes or sprays should help control bots. This treatment should be done once a week for the common bot fly. Since the throat bot fly and nose bot fly have shorter incubation times, treatment should be done two to three times weekly.
There are medications available in the form of liquids and pastes to be mixed in feed
rations or applied orally. Dosages of internal medication are based on weight. Treatments are best given in the colder months after the first killing frost, after bot larvae have started to accumulate on the stomach lining. Alternating classes of insecticides helps combat resistance.

HORSE FLIES AND DEER FLIES
Horse flies (Tabanus sp) and deer flies (Chrysops sp) are serious pests of horses.
These heavy-bodied, brown or black flies are swift fliers and vicious biters. They have clear or striped wings and range from 1/3 to 1 inch in size. These insects feed by piercing the skin of the horse and sucking the blood as it wells up in the wound. Only the adult females are blood feeders and they only feed during the daylight hours. Horse flies and deer flies are usually found feeding on the head, neck, shoulders and back. Horse flies and other blood-sucking insects have been implicated in the transmission of "swamp" fever (equine infectious anemia) in horses.
Most horse flies and deer flies have only one generation per year. The female lays her
eggs on vegetation around moist, swampy places. The larvae burrow into the mud where they spend the next year feeding on small animals. They pupate in the spring and emerge as adults by early summer.
Control of horse flies and deer flies is very difficult. Some control can be achieved by
draining wetlands or by using approved insecticides for larval control. Pyrethrin sprays,
organophosphate and synthetic pyrethroid insecticide sprays give limited control of these pests. These flies do not normally enter structures. Providing pastured horses space and structures for sanctuary during heavy attacks helps alleviate the control problem.

STABLE FLIES
Stable flies, Stomoxys calcitrans, are the most injurious flies that attack horses. This
insect is about the same size of the common house fly, but it is a blood feeder; both sexes feed on blood. Stable flies are usually found feeding on the lower legs or flanks of the horse. Due to the painful bite, horses will stamp and kick trying to rid themselves of these pests. When present in large numbers, stable flies can cause considerable blood loss as well as severe irritation. The flies stay on the animal only while feeding, after which they seek a sheltered area to digest their meal. Females must have a blood meal each time they lay eggs. These flies may contribute to the transmission of swamp fever and are vectors of "summer sores," weeping wounds that are difficult to heal.

Stable flies breed in decaying organic matter. A fermenting mixture of straw, manure and urine is ideal. Although horse manure is usually too dry to support their development, it becomes an adequate breeding medium when allowed to accumulate in stalls or barns where it becomes moistened with urine or water. Decaying straw, grass clippings, hay or silage are also suitable breeding materials for stable flies.

The life cycle of stable flies from egg to adult takes 21 to 25 days. Females can lay up to 20 batches of eggs. High populations can build up under optimum conditions.
Control of stable flies off the animal (in and around buildings, etc.) will be discussed with house fly control. Insecticides may be applied to the animal especially to the legs of the horse. They should be reapplied when they appear to be losing their effectiveness. Under heavy populations, pasture horses away from wooded areas and treat with insecticides every day or two.

HOUSE FLIES
House flies, Musca domestica, are not serious pests of horses, but they are important
disease carriers. These flies transmit stomach worms and have been incriminated in the
transmission of over 60 vertebrate pathogens by body part contamination, regurgitation and defecation. The house fly can cause considerable irritation to the horse when feeding on secretions around the eyes. These flies are 1/4 inch long and dull black or dark gray. House flies feed on a broad range of food and filth including rotting organic matter, garbage, all types of excrement, wet and rotting hay, grass, straw, grain or silage but seem to prefer horse manure. They have a short life cycle of six to 14 days and build up to high populations around stables if not controlled.

CONTROL OF HOUSE FLIES AND STABLE FLIES
A good pest management program is important for stable fly and house fly control.
This includes:
1. elimination of breeding materials;
2. control of moisture;
3. judicious use of insecticides; and
4. mechanical control
3 Elimination of breeding materials --

Good sanitation is the key to any successful fly control program. Corrals, run-in sheds and barns should be designed to facilitate the rapid and efficient removal of manure and other fly-breeding materials. Feed mangers should be designed to minimize the accumulation of wasted feed beneath them. Fly-breeding materials should be
removed and disposed of at least once a week to break the seven to 21-day life cycle of these flies. Make sure areas such as around fence posts, outside and under fences, outside and under feed troughs or hay racks, corners in barns or other buildings, stalls and sick pens, around silos or other feed storage areas, garbage cans and around waterers and water tanks are not missed.
Manure and other fly-breeding materials are most easily disposed of by spreading them
thinly on cropland. This may be done by using a flail-type manure spreader.
Manure storage facilities should be used when it is impossible to spread the manure on
fields. Manure stored in liquid manure pits or manure lagoons should be mixed with enough water to inhibit fly breeding. Agitation of the manure-water mixture will eliminate the accumulation of floating solids where fly breeding can occur.

Manure can be stockpiled in non-liquid type storage areas. However, flies can still
develop in the outer few inches of stockpiled manure. These stockpiles should be well drained. These should be spread thinly on crop land as soon as possible. Large amounts of manure can be composted to reduce fly breeding problems, while creating a useful and valuable by-product.

Moisture Control -- Manure and other fly breeding materials should be kept dry. Corral areas should be designed to promote adequate drainage and eliminate wet spots. Good drainage away from manure stockpiles is also important. Automatic waterers should be maintainedproperly. All these practices promote drying and help reduce fly breeding.

Insecticides -- Insecticides are usually needed to round out a complete fly control
program. However, they should never be the sole means of fly control. There are several ways to use insecticides for fly control.
1. Residual insecticides can be applied to the walls, ceilings and rafters of horse barns, run-in sheds or other farm buildings, as well as vegetation around the buildings will help control adult flies that use these areas as resting sites. Start residual sprays early in the spring where flies first appear. Stop spraying or change chemicals when control is no longer effective. Wettable powder formulations usually give longer residual protection than emulsifiable concentrates when they are applied to bare wood or concrete block walls.
2. Insecticide space sprays, fogs and mists control large numbers of adult flies, especially in enclosed areas such as barns. These chemicals have a short residual effect and must be applied on a daily basis.
3. Insecticide-impregnated strips containing DDVP are useful in controlling adult flies in enclosed areas such as tack rooms, feed storage rooms or box stalls.
4. Insecticide baits available in dry or wet formulations should be spread in areas where flies congregate. Baits should be used daily to maximize their fly control capabilities. Children and domestic animals should not have access to these baits.
5. Larvicides are insecticides that can be applied to areas of intense larval development to kill the larvae before they emerge as adults. These may be sprayed on manure stockpiles or mixed with the feed. Always read and follow label directions. Observe proper safety precautions and avoid contaminating feed, water and equipment with insecticides.

Mechanical Control -- Screening is an excellent way to keep flies out of areas such as feed rooms, tack rooms and box stalls. Fans directing an air blast downward and outward above doors will help prevent flies from entering barns. This integrated approach to house fly and stable fly will control flies and reduce the incidence of insecticide resistant flies. Studies have shown that insecticide resistant strains of house flies develop more rapidly on farms where sanitation is poor. If flies become resistant, intensify your non-insecticidal control measures, rotate insecticides (to another family), and use shorter residual insecticides for adult fly control.

FACE FLIES
Face flies, Musca autumnalis, are occasional pests of horses, especially when the horses are pastured with or near cattle. Both males and females, with sponging mouthparts, feed on mucous secretions of the eyes and nostrils as well as on blood oozing from wounds caused by horse flies or stable flies. Their feeding, especially around the eyes, is very annoying to horses. Face flies are about the same size and coloration as house flies . The female lays eggs in fresh cattle manure. The entire life cycle takes from 15 to 25 days. Face flies are difficult to control because of the difficulty of treating the head. Face flies only stay on the host a short time each day, spending the remainder of their time on vegetation, fence posts or other objects. The use of spray or wipe-on insecticides applied to the head or neck of the horse is the most effective way to control these pests. There are also insecticide impregnated strips and collars that are labeled for face fly control. Wounds should be protected
with dressings or repellents. Fly shakers attached to the halter provide some protection for the eyes. The use of dustbags or face rubbers and insecticide impregnated ear tags are useful in controlling face flies on cattle and help reduce the overall population for horses and other animals.

HORN FLIES
Horn flies, Haematobia irritans, are blood sucking flies that attack cattle and horses if
pastured near cattle. These flies are gray to black and resemble the house fly but are about half as large. They are commonly hand upside down when feeding and are commonly found on the back and sides of cattle and horses. These flies remain on their host day and night, leaving only to transfer to other animals or to lay eggs. Horn flies breed in freshly deposited cattle manure. Eggs hatch in 24 hours and require moisture for survival. The life cycle requires 10 days to one month depending on temperature.
The best way to control them on horses is to control them on cattle. This may be done by using insecticide impregnated ear tags, forced-use backrubbers or regular sprays. Sprays and wipes will provide control on horses as well.

MOSQUITOES AND BLACK FLIES
Several different species of mosquitoes feed on horses. They are slender-bodied, longlegged flies that can be as large as 1/2 inch long. Mosquitoes breed in standing or slow-moving water. They also breed in tin cans, bird baths, old rubber tires or topped-up gutters. Their life cycle is from 10 days to two weeks. Bites from mosquitoes are irritating and large numbers can take large quantities of blood. Only the female feeds on blood. Mosquitoes are a vector of Eastern Equine Encephalomyelitis (EEE) and Western Equine Encephalomyelitis (WEE).
Black flies require moving water. They breed in streams, pond overflows, etc. Black flies bite horses on belly lines, between the back legs and in the ears. Control mosquitoes by eliminating their breeding sites. Sprays and wipe-on insecticides may be applied to horses. Space sprays, fogs and insecticidal strips are useful for mosquito control in stables.

CATTLE GRUBS
Two species of cattle grub, bomb flies (H. bovis) and heel flies (H. lineatum), will
parasitize horses if they are pastured near cattle. Bomb flies are banded with yellow and black stripes, while heel flies are smaller and more orange than yellow. Adults are prevalent during late May through June. Adults do not sting or bite but frighten cattle by their buzzing sound. Females usually lay eggs on the lower portions of the host's body. They hatch in less than a week, penetrate the skin and migrate in connective tissue. Eventually, larvae of both species migrate to the subcutaneous tissue of the back where they cut breathing holes in the hide. When the larvae mature, they escape through the breathing holes, fall to the ground and pupate. Flies emerge during the first warm days of spring. There is one generation per year. Cattle grubs cannot complete their development in horses. They make aberrant migrations to the head, neck, withers and rib cage areas. They remain just under the skin and form hard nodules that may become sores if the horse or the saddle rubs the affected part. These are generally not a problem on horses, However, control of grubs in horses is best achieved by controlling them on cattle. Treatments may be made with an injectable or with organophosphorus insecticides applied as a pour-on, spot-on or spray. Control measures must be applied soon after the fly season is over, which is from late July until November 1.

LICE
Lice can be found on all parts of the horse but are usually first noticed on the head, neck, mane and tail. There are two different species of lice which are occasionally a problem on horses. Signs of lice include scurfy skin, unkempt coat and excessive rubbing and scratching. Lice reproduce all year but are more of a problem during winter. Their entire life cycle is spent on the horse.
The horse-biting louse, Bovicola equi, is about 1/10 inch long and very flat. It has chewing mouthparts and feeds on dry skin, skin secretions and hair. Biting lice lay their eggs around the angle of the jaw and on the flanks. The eggs hatch in five to 10 days. Nymphs begin feeding immediately, reaching maturity in three to four weeks.
The blood-sucking louse, Haematopinus asini, is about 1/8 inch long and a dirty gray
color. Sucking lice are more common, as well as more irritating, than biting lice. They have piercing, sucking mouthparts and with large infestations cause the host to become severely anemic. The horse rubs off patches of hair. Louse infestations are more commonly seen on horses on inadequate diets. Weight loss, stunted growth and susceptibility to diseases are associated with heavy infestations. Lice are not considered important in the transmission of equine pathogenic agents. Eggs are glued to the hairs and hatch in 11 to 20 days. The nymphs suck blood and complete development in two to four weeks. Some animals are particularly susceptible to louse infestation and are known as "carriers". These animals should be routinely inspected and treated, if needed.
Control is achieved by proper grooming, feeding and chemical treatment. Owners usually spot the problem quicker when grooming. Proper nutrition allows the animal to better withstand the blood loss or irritation of a severe louse infestation.
When using insecticides, wettable powder (WP) formulations are generally preferred over emulsifiable concentrates (EC) because some horses are more sensitive to skin burns from solvents in EC formulations. However, problems should not occur if the insecticide is labeled for use on horses for lice and used according to the label directions.

TICKS
In the spring, the American dog tick, Dermacentor variabilis, may infest horses and cattle. Ticks are blood-sucking anthropods closely related to insects. Large numbers of ticks can withdraw a great deal of blood and cause anemia in the host. Ticks cause irritation, restlessness and spread of disease on horses. They can be vectors of sleeping sickness, piroplasmosis and E.I.A. (equine infectious anemia or swamp fever). Ticks may be removed by swabbing them with cotton soaked in alcohol or chloroform. Ticks are suffocated by the alcohol or chloroform. Ticks can also be controlled on horses using the same insecticides used for lice control.

MANGE OR ITCH MITES
Mange or itch mites tunnel in the upper skin layers, suck blood and secondary infections often result. Heavy infestations result in severe dermatitis. Control is achieved by treating the area and surrounding areas on the horse. This treatment should be repeated in seven to 10 days. See materials in table for mange and residual sprays.

CONCLUSION
Adopt a good pest management program, taking into consideration all methods of pest
control available. Plan ahead your pest management strategy. Consult with county agents and specialists in the field. If a chemical does not work, try another in a different family of pesticides. Some insects are difficult to control; but, persistence and well-informed decisions are very helpful.

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