New World Skin Bot Flies Cuterebrinae

Bot Fly Inside Howler Monkey
FIGURE 16.19 Cotton mouse, Peromyscusgossypinus, with mature rodent bot, Cuterebra sp., or "wolf"; posterior end of bot, with posterior spiracles exposed, projecting from location at base of host tail. (Photo by G. R. Mullen.)

normal hosts are rodents (e.g., Microtus, Neotoma, and Peromyscus spp.) and tagomorphs (e.g., Lepus and Sylvi-lagus spp.). At temperate latitudes cuterebrine maggots show seasonal peaks in prevalence. For example, 40% prevalence in Peromyscus populations is not unusual during late summer. Nonnative rodents and rabbits (e.g., Mus, Rattus, Cricetus, and Oryctolagusspp.) also are parasitized, but in these hosts the pathology is more severe and can lead to death of both the host and parasite.

Cuterebra species oviposit in areas close to the center of host activity (e.g., near nests and lairs or along runs). After about 1 week, the eggs hatch in response to a sudden increase in temperature, normally indicating a nearby warm host. First-instar maggots adhere to the host pelage, crawl to natural body orifices of the head, and penetrate the mucosal tissue at such sites as the mouth and nose. After about 1 week in the pharyngeal areas of the host, rhe maggots actively burrow through sheets of host connective tissue to a species-specific, cutaneous site for maggot development (Fig. 16.19). Once there, the maggot cuts an opening through the skin and molts within the newly formed warble. Depending on the bot species involved, maggot development at this site requires 3—8 weeks, during which time the much enlarged maggot can increase some 100,000-fold in weight. When mature, the third-instar larva (Fig. 16.20) backs out through the warble pore and drops to the ground to pupate. After the bot exits, the collapsed warble heals quickly, usually without secondary infection. In cool, temperate regions it is the pupa that diapauses and overwinters, and there is but one adult flight season per year. Warmer areas probably have two flight seasons, where aduits are on the wing during late spring and summer. The adult life span is about 2 weeks.

Dermatobia Hominis
FIGURE 16.20 Rodent bot, Cuterefa-a sp. (Oestridae, Cuterebrinae), third-instar larva, ps, posterior spiracular plate. (Original by E. P. Catts.)

Generally there is little economic importance associated with Cuterebra species, although they can be a seasonal problem in commercial rabbit operations. Sport hunters often discard bot-infested squirrels (Fig. 16.21) and rabbits in the erroneous belief that the carcasses are spoiled by the presence of these maggots. A few

Bot Fly Inside Howler Monkey
FIGURE 16.21 Multiple "wolves" of squirrel bot {Cuterebra. sp.) in shoulder area of gray squirrel, Sciurus carolinensis. (Courtesy of Department of Pathobioiogy, Auburn University College of Veterinary Medicine.)

Cuterebra species have been colonized in the laboratory and can serve as natural bot-host models for the study of bots affecting livestock.

Tórsalo (Dermatobia hominis)

The torsalo is a Neotropical species that occurs widely from southern Mexico to Argentina. Although primarily a pest of cattle, it also infests humans, monkeys, sheep, dogs, other domestic and wild mammals, and occasionally birds (e.g., macaws). This is the only bot fly that frequently parasitizes humans, hence its alternative common name, the human bot fly.

It is a woodland species encountered along forest margins of river valleys and lowlands. It is unusual among cuterebrine flies because of its unique oviposition behavior and means of egg dispersal. Rather than deposit eggs direcdy on a host, the adult female (Fig. 16.22) captures various zoophilic or anthropophilic arthropods, usually dipterans, and glues her eggs in clusters (15—45 eggs) to their abdomen (Fig. 16.23). Embryonization requires 5—15 days. These egg carriers, or "porters," subsequently transport the eggs to a vertebrate host, where they hatch while the arthropod feeds. Among the more common porters are day-flying mosquitoes (particularly Psorophom spp.) and muscid flies (e.g., Sarcopro-musca, Stomoxys, and Synthesiomyia spp.). The newly emerged larvae enter the skin either through the bite puncture or via hair follicles, soft folds of skin, or areas of moist skin in contact with clothing or bedding.

Genes Torsalo
FIGURE 16.22 Tórsalo, or human bot fly, Dermatobia, hominis (Oestridae, Cuterebrinae), adult female. (From James, 1947.)
Figure Black Fly
FIGURE 16.23 A muscid fly "porter" (Sarcopromasca arcaata) to which a torsalo bot fly (Dermatobia hominis) has attached her eggs. (Original by E. P. Catts.)

Development occurs at the point of entry, forming a boil-like pocket, or furuncular lesion, where the larva (Fig. 16.24) undergoes three or four instars. This development usually takes 5-10 weeks but sometimes takes as long as 3 months or more. During this time the narrower posterior end of the larva is extended into the opening at the skin surface where it exchanges air in

Infested Botfly Human
FIGURE 16.24 Tórsalo, or human bot fly, Dermatobia hominis (Ocstridae, Cuterebrinae), mature larva in human skin, with posterior spiracles exposed tlirough hole in skin surface. (From Craig and Faust, 1940.)
Genes Torsalo
FIGURE 16.25 Tórsalo, or human bor fly, Dermatobia hominis; posterior end of maturing larva visible in hole made by larva in skin on human forearm. Note inflammation and swelling at site of wound. (Photo by Ronald D. Cave.)

respiration (Fig. 16.25). After the larva matures, it enlarges the opening and drops to the ground to pupate. The pupal stage lasts 14—24 days.

Other cuterebrine flies

The remaining four genera of cuterebrine flies are tropical and include only a few species. Most of them parasitize rodents, and little is known about their biology. However, the genus Alouattamyia, with the single species Alouattamyia baeri, parasitizes howler monkeys (Alouatta spp.) in Central and South America. This is the only bot fly specific to a primate host. Warbles of this species usually are located in the cervical and axillary regions of their arboreal hosts.

Old World Skin Bot Flies (Hypodermatinae)

These flies are the Eurasian counterpart of the New World skin bots. There are 8 genera and 30 species occurring in rodents, deer, goats, and cattle. All but 2 species are found only in Asia, Europe, and Africa. The most widespread and important species are in the genus Hypoderma, which includes 7 species, 5 causing myiasis in cervids and 2 in bovids.

Cattle grubs (Hypoderma spp. )

The northern cuttle grub (Hypoderma bovis) and the common cattle grub (H. lineatum) (Fig. 16.26) are Holarctic in distribution, having been introduced

Larve Calliphoridae

FIGURE 16,26 Cattle grubs, Hypoderma spp. (Oestridae, Hypodermatinae), third instars. cs, cross section of posterior spiracle of Hypoderma bovis, showing depressed center which contrasts with flat spiracle of H. lineatum; psl, northern cattle grub (H. bovis), third instar; ps2, common catde grub (H. lineatum), third instar. (Original by E. P. Catts.)

FIGURE 16,26 Cattle grubs, Hypoderma spp. (Oestridae, Hypodermatinae), third instars. cs, cross section of posterior spiracle of Hypoderma bovis, showing depressed center which contrasts with flat spiracle of H. lineatum; psl, northern cattle grub (H. bovis), third instar; ps2, common catde grub (H. lineatum), third instar. (Original by E. P. Catts.)

wherever catde are raised. They are major economic pests of domestic cattle. Losses include damage to hides and self-injury by hosts during headlong flights of panic or gadding (Fig. 16.27), in futile attempts to escape ovipositing flies. Thus the name gadfly is often used to refer to the adults. Adults of Hypoderma species also are called heel flies, referring to the defensive behavior of catde in kicking up their hooves.

The biology of H. bovis and H. lineatum is very similar. In late spring and early summer, adult females (Fig. 16.28) of both species glue their eggs directly to host hairs (Fig. 16.29). H. lineatum usually oviposits on the lower body regions of standing or resting hosts,

Bovis Foods
FIGURE 16.27 Gadding behavior of calfin response to attack by heel fly ( Hypoderma bovis), with tail raised and calf kicking up heeJs of hind legs while running frantically about. (Photo by J. Weintraub, Agriculture and Agri-Food Canada, Lethbridge.)

FIGURE 16.30 Multiple warbles along back of cow, caused by Hypoderma bovis (Oestridae, Hypodermatinae). (Photo by J. Weintraub, Agriculture arid Agri-Food Canada, Lethbridge.)

Botfly Canada

FIGURE 16.31 Oestromyia sp. (Oestridae, Hypodermatidae), third-instar larva; causcs myiasis in wild rodents arid lagomorphs. ps, posterior spiracular plate. (Original by E. P. Catts.)

FIGURE 16.28 Heel fly, Hypoderma, bovis (Oestridae, Hypodermati-nae), adult female. (Courtesy of USDA-ARS, Livestock Insect Research Laboratory, Kerrville, TX.)

FIGURE 16.30 Multiple warbles along back of cow, caused by Hypoderma bovis (Oestridae, Hypodermatinae). (Photo by J. Weintraub, Agriculture arid Agri-Food Canada, Lethbridge.)

whereas H. bovis oviposits in the same regions on active hosts. Presence of the latter species is what causes cattle to gad. After an incubation period of 3—7 days, eggs hatch and the first-instar larvae crawl to the base of the hairs on which the eggs were glued. They then penetrate the host skin using their hooklike mouth-parts and proteolytic enzymes. A 4- to 6-month period of burrowing follows as the larvae make their way between sheets of connective tissue within the host. During the winter, first-instar larvae of H. lineatum eventually cluster along the esophagus, whereas the larvae of H, bovis cluster along the spinal column. With the onset of spring the larvae leave these sites and move to the host's back, where they cut a hole, the warble pore, and develop through two subsequent larval instars.

A boil-like warble develops around the enlarging maggot (Fig. 16.30). Mature maggots back out of the warble pore and drop to the ground to pupate. As with all bots, it is at this time of dropping from the host that maggots are most vulnerable to predation by birds, rodents, and insectivores. The pupal stage lasts 1—3 months. Adult flies are on the wing throughout late spring and early summer.

Another Hypoderma species worthy of note is H. tarandi (formerly Oedcma^ena tarandi). In the arctic and subarctic regions, H. t&mndi causes cutaneous myiasis in the backs of reindeer and caribou, similar to that caused by catde grubs. Heavier infestations generally occur in yearling fawns rather than in other age groups. Over time infested animals slowly develop partial immunity to these parasites. Oestromyia species (Fig. 16.31) commonly cause cutaneous myiasis in wild rodents and lagomorphs in Europe, Asia, and the Far East.

FIGURE 16.29 Eggs of heel fly, Hypoderma bovis (Oestridae, Hypodermatinae), attached to body hair of cow. (Courtesy of Agriculture and Agri-Food Canada, Lethbridge.)

FIGURE 16.31 Oestromyia sp. (Oestridae, Hypodermatidae), third-instar larva; causcs myiasis in wild rodents arid lagomorphs. ps, posterior spiracular plate. (Original by E. P. Catts.)

Larve Calliphoridae
FIGURE 16.32 Kangaroo throat bot, Tmckeomyia macropi (Oestri-dae, Oestrinae), third-instar larva; develops in trachea of the red kangaroo, Australia, ps, posterior spiracular plate. (Original by E. P. Catts.)

This subfamily of oestrid flies includes 9 genera and 34 species which parasitize members of the mammalian orders Artiodactyla, Perissodactyla, and Proboscidea (elephants). Most nose bot flies are African or Eurasian in distribution; an exception is the Holarctic genus Cephene-myia. The genera Oestrus (6 species) and Rhinoestrus ( 11 species) comprise the majority of species in this group. Another species, Tracheomyia macropi (fig. 16.32), develops in the trachea of the red Kangaroo in Australia and is the only native bot of that continent.

Nose bot flies differ from other bots in that their eggs develop in utero. The first-instar larvae are squirted by the hovering female direcdy into the muzzle or eye of the host. The larvae crawl down the throat to enter tracheal branches of the lungs, but soon return to the nasal sinuses or pharyngeal region of the host to complete their development. As with other bots in native hosts, there is little pathology at moderate parasite levels. However, purulent mucous exudates associated with an abundance of maggots may lead to respiratory complications or to secondary fly attack. While hosts are under attack by adult nose bots, they stop grazing and attempt to thwart the attack by pushing their muzzles into bushes or clumps of grass. Following development, mature larvae are sneezed from the nostrils of the host, causing some temporary suffering during this time. Occasionally a few larvae may become lodged in the nasal sinuses and can cause the death of their host. After a pupal period of 4-6 weeks, adults emerge and seek a mate at aggregation sites. Adults generally are univoltine in cold regions and at least bivoltine in tropical and warm temperate areas. This indicates that larval development can be delayed during winter and accelerated during summer. Overwintering takes place within the host, as is the case of most other bot flies.

The most widely distributed and economically important species is the sheep nose bot (Oestrus ovis),

Sheep Bot Fly
male. (From James, 1947.)

which parasitizes domestic and wild sheep and goats (Figs. 16.33 and 16-34). Females produce about 500 progeny, which they larviposit in batches of 10-20 at a time. The usual host burden is 12-24 maggots, with gradual attrition reducing this number to fewer than 10 survivors by the time the maggots mature. Other Oestrus species parasitize antelopes in Africa.

The horse nose bot {Rhinoestrus pupureus) is distributed widely throughout Eurasia, Africa, and the Orient. It is most prevalent in Asia, where high population levels of these bots in domestic horses have been recorded (>700 maggots in a single host). High parasite loads can cause death of the host. Ocular myiasis in people who live near, or handle, horses is not uncommon. The general life history of the horse nose bot is like that of O. ovis. Rhinoestrus includes 11 species, 4 in equids and 7 others

Oestrus Ovis Larval Spiracles Images
FIGURE 16.34 Sheep bot, Oestrus ovis (Oestridae, Oestrinae), third-instar larva. (Courtesy of P. Scholl.)
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  • lobelia goodchild
    What is the economic importance of botfly?
    2 years ago

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