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MANAGING EXTERNAL PARASITES

MANAGING EXTERNAL PARASITES Source: Pasture to Market References:· Baldwin, J. L., Foil, L. D., Hogsette, J. A. (2005). Important Fly Pests of Louisiana Beef Cattle · Swiger, S. L. (2012). Managing External Parasites of Texas Cattle The blood-sucking fly pests of Louisiana beef cattle include the horn fly, stable fly and many species of tabanids. Feeding by these flies not only results in blood loss, but it causes annoyance which alters the normal grazing behavior of cattle. The economic impact of these flies is usually attributed to weight loss or reduced weight gain in growing cattle and expenditures for fly control. The biology of these blood-sucking fly pests varies considerably, and this affects the success of various control methods. By understanding the biology and life cycle of each pest, producers will be better able to devise more effective fly control programs. In most cases, an integrated approach, whereby more than one control method is used, will prove more effective for long-term fly control. When utilizing chemical control measures, always read and follow the pesticide label. Horn Fly — Horn flies bite cattle and feed on their blood; they weaken the animal and make it lose weight. The horn fly is about 3/8 inch in length. It is gray and the head of this fly points downward, and the wings are held flat over the back. The females can lay several hundred eggs in their 3-week lifespan. They lay their eggs under the edges of fresh dung pats where they develop in 10–20 days, depending on the temperature.  Adult horn flies have piercing mouthparts and each fly feeds 30–40 times per day. The bites are painful and will form a wound that mars animal hides.  Horn fly populations increase from late spring to early fall; they peak in midsummer. They rest on the withers, back and sides of the cattle, moving to the belly when temperatures exceed 90 degrees F.  When flies exceed 250 per side, calves and yearlings will lose significant body weight (4% - 18%).  To control and prevent horn fly infestations (Non-Chemical):  Drag pastures and spread manure in a thin layer to limit breeding grounds.  Rotate pastures to prevent manure build-up.  The point at which chemical control measures are economically justified is called the threshold. For horn flies, the threshold is 200-250 flies per side. Use chemical control once the threshold is reached. Control options include: Ear tags — Insecticide-impregnated ear tags are applied to the ears of cattle and release a small amount of insecticide over a long period of time. If used properly, they can be an effective tool for controlling horn flies and may reduce face fly populations.  Ear tags can provide about 12-15 weeks of continuous horn fly control.  The active ingredients of ear tags now fall into five broad chemical categories: synthetic pyrethroid, organophosphate, organochlorine (cyclodiene), macrocyclic lactone and mixtures of the synthetic pyrethroid and organophosphate insecticides.  In addition to the active ingredient, several ear tags contain a synergist, such as piperonyl butoxide, that increases insecticide toxicity to the horn fly.  Rotate insecticide classes. Pyrethroid tags should be used no more than once every three years.  Remove insecticide ear tags when they are no longer effective, when the label recommends removal or in the fall. Periodic application methods — sprays, pour-on, self-treatment devices, remote delivery capsule, etc.  Use sprays, pour-on, self-treating devices, etc. with a different mode of action than insecticide-impregnated ear tag, and treat only when horn fly populations exceed 200-250 flies per side. Insect Growth Regulators (IGR) and Larvicides — Insect growth regulators (IGR) and larvicides prevent horn fly larvae from developing into adults. These are administered to cattle as feed or mineral additives; immature horn flies (maggots) are exposed to these chemicals in the manure of cattle which consumed the product.  Some formulations are available ready-to-feed in the form of protein or mineral blocks or tubs, while others will require topdressing or custom blending.  The mode of action of IGRs and larvicides differs. IGRs disrupt normal molting and development of immature horn flies (maggots) whereas larvicides are traditional toxins that kill the maggots.  Use of IGRs or larvicides is normally initiated just prior to the first appearance of horn flies in the spring and throughout the summer and fall until cold weather restricts fly activity.  To be effective, cattle must consume a specified amount, preferably on a daily basis. If consumption is below the specified rate, either increase the number of feeding stations or relocate stations to areas more frequented by cattle. Likewise, if consumption rate is above the specified rate, either decrease the number of feeding stations or relocate stations to areas less frequented by cattle.  Diflubenzuron and methoprene are examples of IGRs; tetraclorvinphos is an example of a larvicide. Stable Flies — Stable flies are serious pests of pasture cattle. They look like house flies but are smaller (3/16 in.). The stable fly is gray with four black stripes on the back, and the abdomen is checkered in black. The stable fly is a blood feeder, mainly feeding on the front legs of cattle but will attack the sides and belly. Their bites are very painful; cattle will often react by stomping their legs, bunch in a group, or stand in water to avoid being bitten. Unlike horn flies that remain on the animal, stable flies rest on nearby surfaces after feeding. Good sanitation practices are key to effective control.
 Stable flies congregate near confined animals and breed in mixtures of urine, manure and decaying litter.
 Larvae (maggots) develop in straw bedding, wet hay, and manure accumulations. Eggs develop into adult flies in 3 to 4 weeks; adults can live for 3 weeks.
 Economic threshold for treatment is reached when concentrations reach 5 flies per leg; however this threshold is often exceeded in Louisiana pastures.
 Larvacides, pour-on and insecticide-impregnated ear tags provide good control.
 IGR developed specifically for horn flies do not affect stable fly larvae due to the fact that stable fly larvae do not grow in manure.
 Sprays have limited effectiveness due to the short amount of time spent on the animal (2-5 minutes) and the location (legs and belly). No spray products have a long enough residual to be effective when sprayed directly onto the animal. Without direct contact mortality is low. Multiple applications may be required. Horse Flies and Deer Flies — The term horse fly is actually a collective common name that includes a multitude of species that belong to an even broader group of flies referred to as tabanids. Deer flies are also tabanids. All tabanids have certain characteristics in common, but these flies vary in appearance and size, ranging from about 1/4 inch to 1 3/8 inches in length. Tabanids are blood-sucking flies that have broad, flat, blade-like mouthparts which inflict a large, deep and painful wound.  Adult female flies require a blood meal to support egg development, but the remainder of the life cycle is independent of livestock.  After feeding, female flies lay from 100 to 1,000 eggs in layered masses on vegetation which usually overhangs some source of water. The eggs hatch in five to seven days. The larvae develop rapidly in warm weather and then leave the water to pupate in drier soil. Adult flies will usually emerge one to three weeks later.  Tabanids and deer flies are perhaps the most challenging livestock pests to control, primarily because of their life cycle. First, most of the life cycle is independent of livestock. The adult female fly is the only link in the life cycle which requires livestock or some other host. But even so, female flies spend only about four minutes feeding on cattle. Therefore, population reduction is very difficult.  Some degree of repellency may be obtained from frequent treatment of a spray mixture of pyrethins & piperonyl butoxide. Use of this mixture may benefit small herd owners in areas of heavy local infestation.
Mosquitoes — Mosquitoes are blood-sucking insects that irritate and stress cattle, thus reducing feed intake. In extreme cases, heavy infestations can result in death through suffocation or heavy blood loss. All mosquitoes require some source of water for the immature stages to develop. Females lay their eggs in water or in places that will eventually be flooded. Once eggs are in contact with water, the life cycle from egg to adult requires about one to two weeks. Only the adult females of most species suck blood. Massive numbers of mosquitoes can build quickly in south Louisiana under certain environmental conditions. Several species of floodwater mosquitoes can develop huge populations when heavy rainfall follows an extended drought. Large numbers of eggs are laid in dry areas, but they remain dormant until activated by rain and rising water. Solitary cattle such as bulls are always the most susceptible to massive mosquito attack. Cattle herds can partially defend themselves by bunching together and lying in mud. If mosquitoes are a serious problem to livestock in your area, control measures should be implemented. The most effective control method available is source reduction by removing or draining mosquito breeding sites. Daily fogging for adult mosquitoes may provide relief, but only as a temporary control measure. Black Flies or Buffalo Gnats — Black flies or buffalo gnats are tiny (1/25 to 1/5 inch in length), dark, stout-bodied flies with a humpbacked appearance. The females are biting flies that require a blood meal to produce and lay eggs. Black flies and buffalo gnats are sporadic, localized pests in Louisiana, but they can be quite damaging when massive outbreaks occur. Eggs are laid in or on the edge of flowing water and the larvae feed on small aquatic life. Adult flies emerge from the water and mate shortly afterward. These flies are vicious biters and can transmit certain diseases. They are most dangerous when explosive outbreaks occur along river basins and streams. Heavy, relentless infestations can kill livestock in a matter of hours. Death is the result of acute toxemia, shock, heavy blood loss or suffocation from inhaling large number of flies. Management practices include the use of smoky fires to repel flies and moving cattle away from the aquatic sources.