Calliphoridae Blow Flies Carrion Flies Floor Maggots Nest Maggots and Screwworms

The most generalized of the six families of Oestroidea is the Calliphoridae, with over 1000 species. Among the members of this large family there is a transition from the facultative myiasis habit by a large number of normally saprophagous species to obligatory myiasis by a relatively small number of species (ca. 100). The larvae typically feed on wet living or dead flesh. Desiccation is detrimental to both egg and larval survival. The following discussion treats the more important, widely distributed, and common genera of myiasis-causing calliphorids.

Carrion-Associated Blow Flies

These are the showy metallic blue-bottle flies, green-bottle flies, and black blow flies (Fig. 16.10). They include members of the genera Calliphora, Chrysomya, Cynomya, Eucalliphora, Lucilia, Paralucilia, Phaenicia, Phormia, and Protophormia, which are commonly associated with dead animal tissues, or carrion. The Old World genus Chrysomya also includes one species that causes obligatory myiasis. The duration of the life cycle of these flies in carrion differs among species but, in general, roughly one-third of the time is spent as the eggs and larvae, one-third as pupae, and one-third as adults from emergence to mating and oviposition. Life cycles typically take 3 to 4 weeks but are prolonged by cold temperatures. These flies are attracted to fetid, purulent open sores and chronic nasopharyngeal or urogenital infections. Heavy larval infestations often result in death of the host, after which the maggots continue to feed on the resulting carrion.

The body form of most of these calliphorid larvae is typical of members of this family (Fig. 16.11) and is

Phrygane EggsMaggot Spiracle

FIGURE 16.12 New World scrcwworm larvae (Calliphoridae), third instars. (A,B) Primary screwworm {Cochliomyia hominivorax), with enlargement of anterior spiracle and darkened portion of large tracheal trunks from posterior spiracles extending into three or four abdominal segments; (C) secondary screwworm ( ('. macstlaria)^ with darkened portion of the tracheal trunks restricted to part of one abdominal segment. (Modified from James, 1947.)

FIGURE 16.12 New World scrcwworm larvae (Calliphoridae), third instars. (A,B) Primary screwworm {Cochliomyia hominivorax), with enlargement of anterior spiracle and darkened portion of large tracheal trunks from posterior spiracles extending into three or four abdominal segments; (C) secondary screwworm ( ('. macstlaria)^ with darkened portion of the tracheal trunks restricted to part of one abdominal segment. (Modified from James, 1947.)

alive. In areas of mild winters, adults can be active during warm spells. In temperate regions screwworm attacks are restricted to the warm seasons, but in the Tropics they are more or less continuous.

Cochliomyia hominivorax (Fig. 16.12A, B) is a major livestock pest, especially to cattle in the Neotropics. Although formerly it ranged throughout tropical and temperate regions of the New World, innovative control measures using male sterilization and baiting of females have eliminated it from the Nearctic. Chrysomya bezziana is distributed widely in Southeast Asia, New Guinea, and Africa. It is the Afro-Asian counterpart of Cochliomyia hominivorax and also is primarily important as a parasite of livestock. Like the American screwworm, this species is attracted to dry, open wounds as well as to most body openings. Generally eggs are deposited in the late afternoon such that their development is completed by the next morning, thereby avoiding lethal exposure to direct sunlight and drying. The rapidly developing maggots consume flesh in localized sites, often penetrating en masse deep into the host tissues, with fatal consequences.

Certain advantages are gained by these flies attacking only living hosts. There is less interspecies competition than among carrion-exploiting species, and the constant body heat of the host enhances maggot development. Additionally, the host tissues are less acidic and more digestible to the maggots than those of fresh carrion.

Species of secondary screwworms are close relatives of primary screwworms but cause facultative, rather than obligatory, myiasis. They are termed "secondary" because they infest wounds only after invasion by primary myiasis-causing flies. The most important species are C. macellaria(Fig. 16.12C) and Chrysomya megacephala. The latter species has become established in the Neotropics and appears to outcompete the former species. Another related blow fly is C. rufifacies. It is a widely distributed carrion-breeding fly that commonly shifts from being a scavenger in carrion to a predator of other maggots. However, on the island of Maui in Hawaii, maggots of C. rufifacies have been known to cause primary myiasis in the umbilicus of newborn calves, with prevalence of infestations as high as 30%.

Nest blow flies (Protocalliphora spp.J

These flies are members of the large genus Protocalliphora (90 species), Holarctic flies whose maggots (Fig. 16.13) are obligatory parasites of nestling birds. The intermittent, temporary blood-sucking habits of these maggots are similar to those of the tropical mus-cid nest maggots. The maggots attach to the host by means of their mouth hooks to feed and then drop free to hide in nest debris while they digest their blood meals. Direct adverse effects on the nestlings are apparent only when maggot numbers are high. There is evidence, however, that their frequent bleeding of the host prolongs nestling development. The longer the time that birds stay in the nest, the more they are at riskofpredation. Maggots thus can indirectly influence nestling success. Many species of Protocalliphora show high host specificity, indicating a long relationship with their respective hosts. These flies seem to favor cavity-nesting birds. Pupation and oviposition take place in the host nest. How the adult fly locates a specific host's nest is unknown.

Congo Floor Maggot
FIGURE 16.13 Nest blow fly, Pi-otocalliphora sp., third-instar larva (Calliphoridae). ps, posteriorspiracular plate. (Original by E. P. Catts.)
2nd Instar Blow Fly

FIGURE 16.15 Congo floor maggot, Auchmeromyia semgaknsii (Calliphoridae), third instar. ps, posterior spiracular piate. (Original by E. P. Cans.)

Larve Calliphoridae
FIGURE 16.14 Tumbu fly, Cnrdylobia anthropophagß, third-instar larva (Calliphoridae). ps, posterior spiracular plate. (Original by E. P. Catts.)

Tumbu fly (Cordylobia anthropophaga,)

The tumbu fly belongs to a small group of African blow flies whose maggots develop in warble-like cysts in hosts ranging from rodents to dogs and people. Rodents are assumed to be their primitive hosts, the flies having become secondarily adapted to other species. Except for their smailer size, these flies have biologies similar to the New World bot flies (Cuterebrinae), in many ways suggesting convergent evolution or a distant relationship.

The adult tumbu fly is yellow-brown in color with two rather broad, but variable, dorsal thoracic stripes. Mature maggots are up to 15 mm in length and densely, but incompletely, covered with small, back-wardly directed, single-toothed spines. The posterior spiracles have a weakly sclerotized peritreme and three sinuous slits (Fig. 16.14). Adults feed on decaying fruits, carrion, and feces. Females are shade-loving and deposit eggs singly in dry sand or dirt contaminated with host urine or feces. Females also are attracted to dry, urine-soiled diapers or clothing. They lay up to 500 eggs over their lifespan of 2—3 weeks. The eggs hatch after several days, following which the first-instar larvae wait in the dry substrate for a host. Contact with a host stimulates the maggots to attach and penetrate the skin. Maggots develop in shallow warbles within or just beneath the skin in about 7—10 days and drop free to the ground to pupate in surface debris. Adults emerge after another several weeks. Although the tumbu fly invades a wide range of hosts, its successful development varies significantly among different host species. The domestic dog is an important reservoir, but maggots develop best in native rodents.

Congo floor maggot (Auchmeromym senegaknsis) The Congo floor maggot (formerly Auchmeromyia Lu-teola), is one of four or five species in this genus causing obligatory, temporary myiasis similar to that caused by Protocalliphora species. They all occur in Africa south of the Sahara, and most are associated with the burrows

FIGURE 16.15 Congo floor maggot, Auchmeromyia semgaknsii (Calliphoridae), third instar. ps, posterior spiracular piate. (Original by E. P. Cans.)

Deer and water buffalo skin maggots (Boopona spp.) These myiasis-causing flies include four species of yellow^brown blow flies whose maggots parasitize the skin of the back and feet of cervids and bovids in eastern Europe, Asia, and the Orient. In the case of cervids, they also attack the soft, developing antler buds. Their eggs are attached singly to hairs of the host and require 3—5 days to develop prior to hatching. These maggots invade the host skin, where they develop individually in warble-like boils in about a 1-week period. Mature maggots drop from the host to the ground to pupate, and adults emerge in 2—3 weeks.

Elephant skin maggot (Elephantolomeus indicus) This species is a small, orange^brown blow fly whose maggots develop only in warble-like boils in the skin of the Asian elephant. Little is known of its biology.

Species of this large, widely distributed family are classified into two subfamilies: the Miltogramminae, which, with few exceptions, are obligatory parasitoids of insects and other arthropods; and the Sarcophaginae, with necrophagous species that include facultative and obligatory parasites causing myiasis. Adults (Fig. 16.16) are typically medium to large, black and gray flies with longitudinal thoracic stripes and a checkered, or tessellated, abdominal pattern. All sarcophagid species are of larger mammals such as warthogs. A. senegaknsis, however, appears to prefer humans as hosts. Adults are yellow-brown in color with markings similar to the tumbu fly. They feed on rotting fruits and feces (e.g., human, monkey, pig). Females can lay up to 300 eggs. The maggots (Fig. 16.15) spend most of their time hidden in loose dirt and floor debris of native huts. At night they crawl to sleeping hosts, scrape or otherwise break the skin, and suck the oozing blood. After feeding for about 20 min the maggots return to hide in debris until the next night. They require two blood meals for each of the three instars and pupate in debris. The life cycle takes about 10 weeks.

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