ORDER DIPTERA
These are the flies. This order of insects is characterized by having 1 pair of membranous wings (when present). The mouth parts function as suctorial organs but there is a great deal of variation between different members of this order. The life cycle usually involved a complete metamorphosis.
Both the adult fly and the fly larvae may be of veterinary significance.
Mosquitoes
There are several important genera of mosquitoes. Many of the numerous species can transmit significant diseases to man and animals. Included in these are such things as yellow fever, malaria, and canine heartworm.
The mosquito life cycle involves eggs that are laid in water. In some species, eggs are laid signally (above, left) while in others, they are laid joined together in rafts. Larvae hatch (wigglers) (above, right) and feed on aquatic material, pupate ( become tumblers) and eventually emerge as adults (above right). Adult females are blood feeders while males are not. Adult females may live several months. Important genera include Culex, Aedes, Anopheles.
Adult male and female mosquitoes can be differentiated from each other based on the presence of bushy antennae in the males (above left). The genus Anopheles can be differentiate from all others by the presence of clubbed palps in the male (above left) (non-clubbed in other species) and long palps in the Anopheles female and short palps in other females (above right). COMPUTERIZED DISEASE VECTOR IDENTIFICATION KEYS
Mosquitos and music - Los moustiques battus
Various control methods are employed against all stages in the mosquito life cycle. Problems exist with all forms of control and continuous applications are usually necessary to produce any effect. Various forms of biological control are presently being experimented with and breeding and selecting for species of livestock that are more resistant to mosquito feeding holds some promise.
Other blood feeding flies
Stomoxys calcitrans - Stable fly
This is a blood-feeding fly that appears similar to the house fly. Eggs are laid in decaying vegetation or manure and larval and pupal stage develop in the same environment, taking about 3 weeks to complete the life cycle. Both males and females are blood feeders and are a serious pest of both man and animals. The stable fly can transmit many organisms including anaplasmosis, anthrax and other blood-bome organisms.
Haematobia irritans - hom fly
Although a small fly, the adult of this species is a pest of cattle with few equals. In the life cycle, the eggs are laid on newly passed feces. In this environment, the complete life cycle take place, usually taking about 2 weeks to complete. The adults are usually present in large numbers along the withers, caudal folds and base of the homs. They remain on the animal all the time (except when eggs are being deposited) but they only feed once or twice a day. Both the adult males and females are bloodfeeders. The adults remain on animal at all times but only feed once or twice a day. The adult fly is usually positioned face down while sitting on the animal. In addition to blood loss with heavy continuous infestations, this fly appears to cause a great deal of irritation and annoyance. Disease transmission includes anaplasmosis and other blood-bome organisms..
Control is usually effective when manure is either removed or dried regularly, breaking the life cycle. Other effective control measures involve anti-larvacidal compounds that are added to the feed or are provided as a supplement. In these latter cases, treatment should be started prior to the fly season.
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Horn Flies Can Bug Your Cattle
Glossina spp.- Tsetse fly
All but one species of Glosssina is restricted to Africa. Both sexes are blood feeders and feed on a wide range of hosts, including man. . Eggs hatch in the female and after larval development, the deposited larvae pupates immediately. The pupal stage lasts about 3 weeks. This fly is a potent vector for several diseases of animals and man including trypanosomiasis..
Musca domestica- house fly
This is perhaps our most common adult fly and although it is a non-biting fly it can be of considerable importance as a pest. Additionally, it has a potential for mechanical transmission of some disease agents due to its presence in decomposing organic and fecal matter. The mouth parts of this fly are modified for lapping up material
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Musca autumnalis - Face fly
This is a non-biting fly that is a serious pest to cattle. It appears to be a recent introduction into North America, first appearing in Oklahoma in 1976. Adults congregate in large numbers around the face of cattle and other large ungulates. It has been implicated in the spread of "pink-eye" among cattle and its presence in large numbers has been responsible for indirect losses in production including reduced milk production and weight gains. The adults are most active from spring through fall.
Simulium sp. - Black fly; buffalo gnat.
There are many species in this genus. The adult fly is small (I -5 mm) and prefers to lay eggs in swift running water. Eggs are deposited on objects on or near the surface of the water. After the eggs hatch (1-4 weeks) larvae attach to the submerged objects and remain there for about a month. After the larval stage pupates, adults emerge in about a week. Although small in size, the adults are good flyers and may go several miles in search of food. Only adult females are blood feeders. In the U.S., Leucocytozoon spp is the major pathogen transmitted by this genus. Simuliidae - Black Flies
Phlebotomus spp- sand flies.
The breeding places for this genus appear to be mainly non-aquatic situations. It is an important vectors for some species of Leishmania.
Culicoides spp - No-seeums, punkies, biting midges.
The life cycle for this genus involves aquatic breeding places, primarily temporary pools. It is an important vectors for blue-tongue virus in many animal species as well as being a pest. Only females are blood-feeders.
Melophagus ovinus- Sheep
Ked or sheep "tick". This genus is one of the hippoboscid flies. The adult hippobosids are blood feeders and are well adapted to an existence on wool, hair and feathers. The life span of this fly is about 4 months with adult females retaining larvae internally until pupation. Pupae are attached directly to the wool. The entire life cycle of this fly takes place while on the infested animal. Keds may be found on the infested animal at all times of the year. Other hippoboscid flies are important vectors for some avian diseases such as Haemoproteus spp. .
The sheep ked, Melophagus ovinus, was once a serious pest in the sheep industry. Use of injectable antihelminthics also effective against some arthropods have made this a less frequent problem. Several similar genera are present on wildlife including deer and elk.
MYIASIS PRODUCING DIPTERA LARVAE
Myiasis is the term used to describe the invasion of tissue by fly larvae. Such invasions can be benign in effect but others may result in a variety of conditions, including death. When the invasion occurs in the intestinal tract, it is called intestinal myiasis; the stomach, gastric myiasis; nasal myiasis,; cutaneous myiasis, etc. Some species of flies that are not significant as adults are important to veterinary medicine as myiasis producing larvae.
Identification of fly larvae to the generic level depends on microscopic evaluation of various anatomical features. Most importantly of these is the spiracle openings, located on the posterior of the larvae (shown below). Diagnosis can be made on both the size of the larvae, location and host from which it was recovered,, and characteristics of the spiracle openings.
Warble flies of cattle are perhaps one of the most significant myiasis producing problems of the cattle industry. Although a common problem for many years, new control programs and products make this a treatable and controllable problem.
There are two important species of the cattle grub, Hypoderma lineatum - the Southern cattle grub, and Hypoderma bovis - the Northern cattle grub. The former is found throughout the country while the latter is restricted to northern portions of the country. In Oklahoma, both species can be present.
The general life cycle for this species involves adult flies depositing eggs on the body of the host. Eggs are glued to hairs. The Eggs hatch in several days and penetrate the skin. Larvae migrate through tissue and congregate at the wall of the esophagus (below right). From here they migrate to the subcutaneous tissue of the back and remain on back for several months after which time they fall out to the ground where they pupate. Adults are present from February to June. Larvae migration is from June to October with larvae being present on the back of cattle during October and November. The pupal period is generally from December to February. The fly free date (the time when adult fly activity ends) is generally the middle of June in Oklahoma. There are several direct and indirect causes of injury and economic loss that can be attributed to infestations with this larvae. Mortlities can occur during larval migration and when they are congregated in the esophagus area. Indirect losses are reported as reduced milk production, loss of weight or poor weight gains, and reduced value of the carcass and/or hide due to larval presence.
The cattle warble is over I inch in size (when on the back) and spiracle openings lack slits and posses non-central button (below left).
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Cuterebra spp. Common warble of rodents and rabbits.
Although common in wild rodents, infestations with this larvae are also occasionally seen on dogs and cats. Most cases are seen during the summer months when fly activity is highest. Typically, cases in domestic animals involve a single larvae. The life cycle is similar to that of Hypoderma with larvae moving to various locations on the body of the infested animal. One species (Cuterebra emascularer) parasitizes the external reproductive organs of rodents and may have a effect on population numbers (below right).
The larvae, when seen on the cutaneous surface, (below, left) is another large larvae with spiracle characteristics similar to Hypoderma only each spiracle is divided into several plates
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Ostrus ovis - Sheep bots or head grubs.
This is a common bot that invades the nasal passages and sinuses of sheep. Adult flies deposit living larvae on the nasal passages where they work their way into frontal sinuses attaching themselves to the mucus membranes. They remain in this location for several months eventually falling out (or sneezed out) and pupating on the ground. The pupal stage lasts about three to six weeks. Once infested, there is usually a purulent discharge from the nostrils, vigorous shaking of the head, loss of appetite, and grating of the teeth. Most cases do not result in pronounced clinical signs although death can occur within a week of aggravated signs. The indirect losses and aggravated condition resulting from infestation is perhaps the best reason for treatment. The large larvae (below left) is similar in appearance to Hypoderma with the exception that the button in the spiracle opening is centrally located (below right).
Gastrophilus spp - The Horse stomach bot.
There are several species of this parasite each of which has slightly different locations of attachment.
The adult flys are common in mid-summer. Females deposit eggs on hairs usually on the forelegs, belly, flanks and inside the knees (below, left). Friction and moisture cause eggs to hatch when the horse licks these areas.. Larvae migrate to the mucus membrane of the tongue and lips eventually making their way to the stomach or other locations (below, middle and right). Here they remain attached until the following spring when they detach and pass out with the feces to the ground and pupate. Several direct and indirect pathologic changes are associated with infestation. While moderate infestations of bots will give no outward signs, heavy infestations might be indicated by digestive disorders. Possible interference with digestion and absorption of nutrients, obstruction of the pyloric spincter and irritation of the mucus membranes are all common.
Cutaneous myiasis
Primary screw worm is of important since larvae will invade live tissue. Although this species is considered eradicated from the U.S. it is still common on our southern order and many other locations throughout the world. It was successfully controlled in the U.S. by use of "sterile male" program. Factors that influenced the success of this program include 1) flies are cold sensitive (will not over winter if temperature drops below 49 F for more than 3 months), 2) males are polygamous and females monogamous, 3) life cycle is about 4 months.
The gravid female screw worm fly is attracted to ovipositon sites on living animals. These sites are any wounds, bites, discharges, etc. that may occur. The naval of newborn animals is a common location for egg deposition. The eggs hatch in 24 hours and larvae enter the wound and begin feeding. The larvae burrow into tissue, enlarging the wound. Animals smaller that rabbits usually do not survive infestations. Larger animals may succumb to repeated infestation or if larvae penetrate blood vessels. Death is usually caused by toxemia and/or septicemia from bacterial invasion of the wound. In addition to the continued release of sterile males, a Screwwonn Adult Suppression System is now used which involves a chemical attractant with dichlorovos. Identification of larvae involves evaluation of the spiracle openings (below left) and the determination of tracheal trunk pigmentation in C hominivorax (below right).
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Blow flies - Many species of necrotic tissue feeders.
These are important parasites because they are common and able to parasitize wounds and abrasions on animals. "Blowfly strike" is common in sheep and other animals. All are non-live tissue feeders and larvae develop in decaying organic material. Identification of larvae depends on morphologic characteristics of the spiracle openings. In many cases, differentiation from primary screwwonn is of importance.
Several species of blowflies are important in outbreaks of avian botulism or "Limber-neck". Outbreaks are common in both free-ranging and captive birds. Dead birds serve as a food source of developing maggots which concentrate the toxin and serve as a means of infection and food for other birds.
Treatments
Various treatments are available depending on the situation and the parasite involved.
Adult Diptera are generally controlled by spray application of products such as Malathion and Pyrethrins. Application can be directed at adult flies or applied to premises.
Fly larvae can be controlled by various means, depending on their location.
Most myiasis producing larvae are effectively controlled with Ivermectin during the migratory phase of their life cycle. Various organophosphates (sprays, topical, etc.) are also available. The timing of treatment can be important as killing migrating larvae at specific locations in the body may result in pathologic changes and tissue reactions.
Various feed additives and supplements are also available for the treatment of void feces as a means of controlling Diptera larvae that are coprophagic.
Cattle grub treatments
Chemical Application RemarksCoumaphos Pour on Do not use with pyrethroids
(Co-Ral) 1/2 oz/cwt
Famphur Pour on Many restrictions
(Warbex) 1/2 oz/cwt
Fenthion Pour on & Many restrictions
spot-on
Ivermectin Injectable & IM application
pour on
Trichlurfon Pour on For animals
over 3 months
Pesticides for livestock to control flies Chemical Application RemarksDichlorvos Residuale,spray, bates Use outside for direct application Fenthion Spray Same Permethrin Spray Same Pyrethrins Spray,aerosol Same Methomyl Bait Stirofos Spray, feed additive Larvaside on manure