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Fly control
Flys affecting livestock
By Clifford E. Hoelscher, Carl Patrick, James Robinson
Oct 28, 2002, 11:01am

Livestock Pests

House Fly
The house fly is suspected of reducing weight gains and feed efficiency in livestock. Pesticides alone will not control house flies. Sanitary measures that eliminate fly breeding areas such as spreading of manure, regular cleaning and prevention of was te accumulation and regular removal of spilied feed are necessary. Spread manure thinly in fields so fly eggs and larvae will be killed by drying and heat. Several pesticides can be used on manure piles to prevent maggot development.

Pesticides in spray or bait forms may be used to control adult flies in livestock barns and poultry houses. Do not contaminate feed, utensils, drinking water or milking equipment with any pesticide.

Stable Fly
Stable flies suck blood, irritate animals and reduce weight gain and milk production. These flies breed in mixtures of manure and decaying litter around barns. Dispose of manure and litter as outlined for house flies. Sanitation is important in reducin g stable fly numbers. Immediate fly control may be obtained by spraying fly resting areas with approved pesticides.

Screwworm Fly
The screwworm fly has been eradicated from Texas. The last confirmed case was reported in 1982. Eradication was accomplished over a 20-year period using sterile-male fly releases, insecticide baits and producer diligence and support. Screwworm eradicat ion has now been achieved in the Republic of Mexico. Eradication efforts are presently underway in Costa Rica and Panama.

There is a constant threat of reintroduction of the screwworm by the accidental transportation of infested animals to uninfested areas. Producers must always be aware of the potential threat of screwworm infestations. Producers are urged to inspect livest ock for screwworms and submit all suspect blow fly larvae found in animals for positive identification. Collect 10 larvae from deep within the wound. Place them in alcohol and send samples to the Southwest Screwworm Eradication Laboratory, Box 969, Missio n, TX 78572. Telephone (409) 845-7027 at Texas A&M University for additional information. The USDA, APHIS, international services office at (301) 734-8892 also can provide assistance. Suspect screwworm samples can be sent directly to the National Vete rinary Science Laboratory, Box 844, Dayton Road, Ames, IA 50010, (515) 239-8301.

Report any suspected screwworm cases to your county Extension agent or local veterinarian. Eradication personnel can take the appropriate measures only when they are aware of the problem.

Horn Fly
Horn flies suck blood, irritate cattle and reduce weight gains by decreasing animal thrift and vigor. Horn flies can become numerous on cattle from late spring to early fall. There are several self-treatment devices that may be used to control horn fli es. Cable-type back rubbers covered with an absorbent material treated with an insecticide-oil solution, or fabric dust bags partially filled with an approved pesticide dust, have been used successfully. Place these devices near water, feed or mineral sou rces or in gaps or gateways to encourage use. A 2to 3-week adjustment period may be necessary before cattle begin to use self-treatment devices regularly. Forced use of these self-applicating devices results in more rapid and effective control of horn fli es and may aid in lice control.

Insecticide-impregnated ear tags provide excellent horn fly control for periods of 2 1/2 to 5 months if properly attached to the ear and if pyrethroid or organophosphate resistance is not a factor.

Automatic, animal-activated sprays often are installed in exit chutes of milking barns. Animals can be treated conveniently twice each day (or less often as necessary) with very small volumes of specially formulated pesticides for biting fly and other ins ect control.

Management of Pyrethroid-Resistant Horn Flies
Field observations and laboratory studies conducted during the summer and fall of 1984 confirmed the development of pyrethroid resistance in horn flies. The combination of very effective insecticides and widespread ear tag use by cattlemen has allowed horn fly resistance to develop. Cross-resistance to the common pyrethroids has been confirmed by field observations. Flies that have developed resistance to one of the pyrethroids will be resistant to all other pyrethroid insecticides currently labeled fo r use in Texas. However, the newer products may continue to provide acceptable control for several years by using more potent materials.

Continued treatment of successive generations of flies with the same type of insecticide can cause insecticide resistance to develop. Individuals in the population that are carrying genes susceptible to the toxicant are quickly killed, and the survivors, carrying resistant genes, reproduce to build the next, more difficult . kill generation. Rotation of insecticides with different modes of action is extremely important in avoiding or delaying resistance.

Insecticide ear tags perform by dispensing a small amount of the insecticide continuously over a 2 1/2- to 5-month period. The insecticide diffuses to the tag surface and is deposited on the animal's body through normal body movement. Flow of the insectic ide from the tag starts at a high rate and decreases to a point where fly control is no longer achieved. Ear tags have provided economical control of the horn fly, Gulf Coast tick and spinose ear tick. Data show that horn flies are the most obvious pest t hat can become resistant to pyrethroid insecticides dispensed from ear tags.

The following are management options for control of pyrethroid-resistant horn flies:

Option 1: Do not treat cattle for horn flies.
Option 2: Treat cattle with insecticides only after horn fly populations reach 250 to 300 per head. Research has indicated that if there are fewer than 250 flies per animal, economic losses rarely occur.

Treatment Options:

a) Use alternate chemistry type sprays, dusts or other formulations. Treat only when horn fly populations exceed 200 to 250 per head.

b) Use organophosphate (OP) ear tags such as Cutter 1®, Terminator®, Optimizer® or Commando®. Do not use organophosphate ear tags if they have been used the previous 2 or more successive years. If ear tags are used, remove tags when calves are weaned or cows are worked in the fall. If horn fly populations exceed 200 to 250 per head at the time tags are removed, apply a spray or dust treatment to reduce the potential population of overwintering flies. Where there are flies resistant to pyrethroid or OP insecticides, continued use of these chemistry types can increase resistance levels. Do not use pyrethroids in any formulation including organophosphate/ pyrethroid combination ear tags where resistance is a problem. Left untreated, susceptible flies will mate with other susceptible or resistant flies. This reduces the rate at which resistance develops. Periodic application methods tend to increase resistance levels less than continuous release methods. The combination ear tags include Double Barrel® and Max Con®. These dual chemistry tags are not listed because resistance develops for both types of compounds.

Blow Fly
Blow fly larvae, commonly referred to as fleeceworms or wool maggots, attack sheep and goats. Infestations usually start around the crotch in wool or mohair contaminated with feces and urine. Ordinarily, tagging and docking animals prevents fleeceworm infestations. If fleeceworms occur, shear the affected area and treat with a labeled insecticide.

Blow fly maggots also are found in wounds on other livestock. Black blow fly larvae frequently infest dehorning wounds during winter months and occasionally infest the navels of newborn animals.

Cattle Grub (Heel Fly)
Cattle grubs cause economic losses because they reduce milk production, weight gain, feed efficiency and hide value. Losses also are suffered with carcass trim and lower meat quality.

Cattle grubs are the larval stage of heel flies. Adult heel flies emerge in late winter, spring or summer. Female flies lay eggs on the legs and lower body regions of cattle. Heel fly activity causes cattle to run widely with tails in the air [gadding), o r to stand in water to protect themselves. Eggs attached to the hairs hatch into tiny larvae that penetrate the skin and begin to migrate through the body of the animal. Larvae congregate in the tissues of the esophagus, but eventually move to the back in later summer, fall or winter. Grubs develop with a "cyst" or "warble" just under the skin on the back. After 6 to 8 weeks, grubs leave the animal's body through holes cut in the hide, fall to the soil and pupate.

Although cattle grubs can be controlled after they reach the animal's back, earlier control is preferable. Once the grubs reach the back, most of the damage has been done.

Systemic pesticides administered as sprays, dips, pour-ons, boluses and injectables are distributed through the animal's body; systemic pesticides destroy cattle grubs by contact action. To avoid the possibility of a host-parasite reaction, cattle should be treated with systemics as soon as possible after heel fly activity ceases but not within a 6- to 7-week period prior to the expected appearance of grubs in the back. Typical host-parasite reaction symptoms include a swollen esophagus, bloat, profuse sa livation, discomfort and, in extreme cases, death. Do not confuse a host-parasite reaction with organophosphate poisoning, which is quite similar. Atropine, an antidote for OP poisoning, is NOT RECOMMENDED for a host-parasite reaction and may make the pro blem worse.

Bot Fly
Two species of bot flies attack horses. With heavy infestations horses become unthrifty. Eggs are attached to hairs on the lip and under the jaw or on the front legs of horses, depending upon the bot fly species. Eggs hatch directly or in response to w armth and moisture, usually where horses lick themselves. Larvae become attached to and feed in various portions of the digestive tract, from the mouth to the rectum. Mature larvae are passed with the feces. Pupation occurs in the soil and adults emerge 3 to 10 weeks later. Treatment for bots is an oral dose of an approved pesticide.

The sheep nose bot is a hairy, yellowish fly about the size of a honey bee. It deposits living larvae around the nostrils of sheep. The larvae crawl into nasal passages where they remain until mature. After varying lengths of time, they fall to the ground where they pupate

Horse Fly, Deer Fly, Mosquito, Black Fly
Horse fly and deer fly adults are vicious biters. They cause livestock to lose weight and may transmit anaplasmosis, anthrax and other diseases. Most horse flies and deer flies are found in brushy or low lying pasture areas near creeks, streams or tank s that provide damp soils in which the immature stages develop. Moving livestock from such areas may provide them some relief from the attacks of horse flies and deer flies.

Mosquitoes are important pests of livestock in irrigated areas or where there is heavy rainfall. Producers may not fully appreciate the losses that mosquitoes cause, for heaviest attacks often occur at night. Mosquitoes are carriers of several diseases, i ncluding sleeping sickness in horses.

The black fly is a small humpbacked fly which can occur in tremendous numbers, causing irritation and even death to livestock. They are important vectors of diseases such as leucocytozoan disease of turkeys. Smokey fires can give animals relief from black flies. Insecticides also give temporary relief if applied frequently. Larvae develop in rivers and streams. Larvacidal control requires careful study and the accurate application of insecticide.
The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.

Educational programs conducted by the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disability, religion, age or national origin.

Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30, 1914, in cooperation with the United States Department of Agriculture. Zerle L. Carpenter, Director, Texas Agricultural Extension Service, The Texas A&M University System.

8M, 8-97, Revised

ENT;AS 1;PS 1-2


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