Common Species Of Hippoboscids

A number of louse flies in the genus Hippobosca are of particular interest to veterinary entomologists. Most

Sheep Ked Drawing
FIGURE 17.5 Sheep ked, Melophagus ovinus (Hippoboscidae), female, dorsal view. {Courtesy of Cornell University Agricultural Experiment Station.)

occur in Europe, Africa, and Asia. Occasional introductions have been made into the United States with the importation of zoo animals. With the exception of the ostrich louse fly (Hippobosca struthionis), they are primarily parasites of mammals. The sheep ked (M. ovinus) is a parasite of sheep and is considered one of the most important insect pests of sheep in many areas of the world.

Sheep ked (Melophagus ovinus) The sheep ked (Fig. 17.5) is a wingless ectoparasite that spends its entire life on domestic sheep. It is worldwide in distribution except in tropical regions, where it occurs only in the cooler highlands. It probably was introduced into the United States in the 15th century, shortly after the European discovery of the New World. Often called the sheep tick by sheep producers, it is found on both range and farm flocks of sheep. The sheep ked is of considerable economic importance and is generally regarded as the most damaging ectoparasite of sheep in North America. A relative of the sheep ked, M, montanus, occurs on Dall's sheep (Ovis dalli).

Much of what is known about the life history of hip-poboscid flies is based on studies of M. ovinus. After a period of 7—8 days of feeding and growing in the uterus of the female, the fully developed larva is deposited and cemented to the sheep's wool. Members of the genus Melophagus are the only hippoboscids to attach their larvae to the host. The reddish, barrel-shaped puparium

FIGURE 17.6 Puparium of sheep ked, Mdophagus ovinus (Hippoboscidae), adhering to sheep wool. (Courtesy of J. E. Lloyd.)

(Fig. 17.6) is fuily formed within 12 hr of parturition. In Wyoming, Swingle (1913) determined that the duration of the pupal stage varied from 19—23 days in summer to 20—36 days in winter. The variation of this period was attributed to differences in temperature and the distance of the pupa from the skin of the host. Slightly shorter periods have been reported in areas that are warmer than Wyoming. Swingle further indicated that the duration of the pupal stage is unlikely to be less than 19 days even in the warmest climate and may increase to 40—45 days in the winter.

Teneral females of the sheep ked mate within a day of eclosion, although the first larva is not deposited for at least 12 days. This period includes 6—7 days for larval maturation. Although one mating provides sufficient sperm for a lifetime, repeated matings usually occur when multiple males are present. A female sheep ked normally lives about 4 months and produces 10—12 larvae during its lifetime. Some, however, can live for 6 months or more and can produce 15—20 larvae. The male life span is slightly shorter, approximately 2—3 months.

Larviposition by the sheep ked tends to occur on lower body parts, especially under the neck and in the breech area. In unshorn sheep, adults are consistently most numerous in the rib area. Contrary to popular belief, there is no daily or seasonal movement from one location to another on the host. In the spring and summer, sheep keds are more likely to be found on the underside of sheep that have been recently shorn and on young lambs with a very short fleece. Often they can be found in tufts of longer fleece missed by the shears. Numbers of keds tend to be greater on younger animals.

Sheep keds generally live for only a few days if removed from the host. However, they may live up to 5 days in wool in the laboratory and, when kept under cool and moist conditions away from the host and fleece, they may live even longer. Their vigor and ability to relocate a host diminish the longer they remain separated from a host animal.

Although sheep keds that become dislodged from their host have the ability to locate a host from the ground, transfer of sheep keds is primarily by animal-to-animal contact. Newborn lambs become infested with keds directly from their mothers soon after birth. Within a flock, transfer occurs when sheep keds move to the tips of the fleece in response to increasing air temperature and possibly in response to the brisk movement of sheep that accompanies flocking behavior. Air temperature usually must be 2l°C (70°F) or above before many sheep keds are observed on the surface of the fleece. At 27-58°C (80—90°F) sheep keds are common on the outer woo! surface. Thus, transfer between animals is more likely, and occurs more rapidly, in summer than in winter.

Like many ectoparasites, populations of M. ovinus exhibit annual fluctuations in their numbers. Although minor variations have been reported from different parts of the world, populations of the sheep ked tend to be highest from late winter to early spring and lowest in summer. In Wyoming, ked numbers on ewes tend to increase from September to February. Periods of high populations are extended on rams, pregnant ewes, and undernourished animals, with increases in numbers being prolonged for several weeks in pregnant ewes (Nelson and Quaily, 1958). On newborn lambs, which receive only teneral keds from their mothers, numbers of sheep keds increase from their birth in early Spring to a couple months later, when populations begin their normal decline. Seasonal decline of sheep ked populations is attributed to acquired resistance (Baron and Nelson, 1985; Nelson and Bainborough, 1963). This resistance is apparently caused by a long-lasting, cutaneous, arteriolar vasoconstriction that cuts off much of the capillary blood flow to the upper dermis. Keds are unable to obtain sufficient blood and die of starvation.

Sheep keds feed approximately every 24—36 hr, with the feeding time increasing to 2-day intervals as the keds become older. The feeding period of an individual ked is typically 5—10 min. Feeding is from larger vessels (30— 100 |xm) near the bases of the wool follicles and often near the apocrine glands or sweat glands associated with primary follicles (Nelson and Petrunia, 1969). Penetration of the dermis by the mouthparts is accomplished by rapid and continuous movement of prestomal teeth on the labellum, followed by movement of the entire haustel-lum. After piercing a blood vessel, the mouthparts are secured in place by the prestomal teeth, which are everted and serve to anchor the labella to the vessel wall.

Dog fly (Hippobosca longipennis)

The dog fly originally was a parasite of wild carnivores in East Africa. It has since become widely distributed in

FIGURE 17.7 Horse ked, Hippobosca equina (Hippoboscidae), female, dorsal view. (From Hutson, 1984.)

association with domestic dogs from southern Europe and the Mediterranean region to China. It appears best adapted to warm and arid climates. Up to one-third of dogs in parts of Egypt are infested with this louse fly. It is found mainly on dogs in the Palaearctic region and on wild carnivores in Africa. It has been recorded from the families Canidae (dogs, foxes), Viverridae (mongoose, civet), Hyaenidae (hyena), and Felidae (cats).

In 1972 H. longipennis was introduced into North America on captive cheetahs from Africa. Subsequently the species has been detected in the United States on cheetahs at wild animal or safari parks in California, Texas, Georgia, and Oregon. Efforts were made by officials in each of the affected states to eradicate this ectoparasite before it escaped from its introduced host to domestic pets, livestock, or wildlife. There is no evidence that this species has become established in the United States or elsewhere in the New World.

Hippobosca equina

This species (Fig. 17.7) is normally a parasite of Equidae (horse, donkey, ass) and is a facultative parasite of catde. Although widely spread in the Old World (Europe, northern Africa, western Asia), it does not occur on wild hosts. The original hosts are unknown. H. equina, is a serious and common pest of a wide variety of domestic animals in Egypt (Hafez et aL, 1977). It can torment its hosts with painful bites and possibLy act as a vector of disease agents, including those that cause piroplasmosis of horses, Q fever, and other types of rickettsioses.

Hippobosca variegata

Tropical Africa is probably the center of distribution of this species, from which it has spread northward to the Mediterranean and eastward into Asia. It is normally a parasite of the domestic horse and its relatives

{Equus spp.) and cattle (Bos spp.). H. variegata is also reported from camels, dromedaries, and water buffalo in Africa and Asia, but these are considered facultative hosts.

Deer keds (Lipoptena and Neolipoptena sppj

Three species of Lipoptena and one of Neolipoptena are parasites of deer in North America, where they are called deer keds. In western North America Lipoptena depressa and Neolipoptena ferrisi are frequently found on the same host. The wings of deer keds are deciduous. They are fully developed and functional in the newly emerged adult, or volant, although the wing venation is greatly reduced. The wings are shed, probably within 48 hr after the ked reaches a suitable host. Pre-pupae are deposited while the ked is on the host but eventually fall to the ground.

Lipoptena depressa

According to Bequaert (1957), L. depressa is the usual and common parasite of several races of Odocoileus hemionus. These include the Rocky Mountain mule deer (O. h. hemionus), the Columbian black-tailed deer (O. h. eolumbianus), the California black-tailed deer (O. h. californieus), and probably the southern black-tailed deer (O. h. fulginatus). It also probably parasitizes the western white-tailed deer (O. virginianus leucurus). Both deer species are efficient breeding hosts. L. depressa is present along the Pacific Coast from southern British Columbia to southern California and as far inland as Alberta (Canada) and western South Dakota and Nebraska. Its range includes most of the Rocky Mountain states but apparently not Arizona and New Mexico.

L. depressa has been divided into two subspecies: L. d. depressa and L. d. pacifica (Maa, 1969). L. d. depressa is limited in its distribution to the eastern slope of the Rocky Mountain highlands in western Montana, northern Wyoming, southwestern South Dakota, and northwestern Nebraska. The normal host is the Rocky Mountain mule deer. L. d. pacifica is found on the western slopes of the Rocky Mountain lowlands, including British Columbia (Canada) and the states of Washington, Oregon, Idaho, and California. L. d. pacifica normally breeds on Columbian black-tailed deer and the western subspecies of white-tailed deer.

L. depressa volants will alight on any moving object. Most leave quickly, however, without dropping the wings if they land on an accidental host such as humans or horses. Westrom and Anderson (1992) found that L. depressa was a bivoltine species in California, with volants appearing in peak numbers in October and April. On the host, peak populations of apterous adults occurred in midsummer and early winter following adult

FIGURE 17.8 Deer ked, Lipoptena cervi (Hippoboscidae), females, dorsal view. (A) Winged (alate); (B) wingless (dealate). (From Hutson, 1984.)

flights. Thousands of L. depressa may be found on an individual deer, with populations especially heavy in the fall.

Lipoptena cervi

This deer ked (Fig. 17.8), is a common parasite of the true elk (Alces alces), red deer (Cervus elaphus), and other species of deer in Europe. In the United States it was first reported from New Hampshire and Pennsylvania in 1907. It now occurs in New York, New Hampshire, Massachusetts, and Pennsylvania. Bequaert (1942) believed that L. cervi was introduced into North America by humans with deer from Europe, and the species subsequently spread to white-tailed deer (O. virginianus). It also has been reported from another host native to the United States, the wapiti (C. canadensis).

Swarms of newly emerged, winged L. cervi appear in the fall, but apterous keds may be found on the host year-round. In Russia mass emergence is observed late in August and the first part of September (Chistyakov, 1968). They are most active on warm, clear afternoons. They are concentrated in low places protected from the wind, in young deciduous forests. The puparia remain on the ground in areas where their hosts are normally found until they emerge in September. Puparia may be particularly numerous at wallows and places where the hosts rub and shed their winter coats.

Lipoptena mazamae

This species is a parasite of white-tailed deer and brocket (Mazama spp.). The range of this tropical insect extends northward from Argentina through South and Central America into the United States, where it occurs in the states bordering the Gulf of Mexico and along the Atlantic coastal states to South Carolina. In surveys of white-tailed deer in southern Texas and Florida, it was the most prevalent ectoparasite (Forrester et al., 1996; Samuel and Trainer, 1972). Volants may be active in every month from April through November. Numbers on the host appear to be significantly lower in the fall than in the spring or summer. Low populations of this species have been attributed to mortality of the puparia in areas of flooding or high rainfall.

Neolipoptena ferrisi

This species occurs in the western United States from Canada to Mexico. Its range includes California, Oregon, Washington, the Rocky Mountain States, and as far east as South Dakota. This deer ked occurs on three races of O. hemionus: the Rocky Mountain mule deer (O. h. hemionus), the coastal black-tailed deer (O. h. columbianus), and the California black-tailed deer (O. h. calif or nicus). Bequaert (1957) considered O. hemionus to be the only true breeding host of this insect and regarded records from western white-tailed deer (O. virginianus leucurus) and prong-horn antelope (Antilocapra americana) as accidental occurrences.

In dual infestations, N. ferrisi is normally outnumbered by L. depressa. N. ferrisi tends to be collected most frequently from the anterior regions of the body, with the highest population density on the head, whereas L. depressa is collected most frequently from the posterior regions of the body, including the tail (Westrom and Anderson, 1992).

Pigeon fly (Pseudolynchia canariensis)

The pigeon fly (Fig. 17.9) is a winged hippoboscid that was introduced into North America at least a century ago. The earliest record in North America is 1896, when it was taken on pigeons at Savannah, GA (Knab, 1916). Its distribution now is nearly cosmopolitan. This is the only species of hippoboscid that parasitizes domesticated birds. In North America, it is found only on domestic pigeons (Columba livid). In the Old World it occurs both on domestic pigeons and on birds of several other avian orders. Juvenile birds are more frequently attacked. Heavily infested birds become emaciated and susceptible to

FIGURE 17.9 Pseudolynchia canariensis (Hippoboscidae), female, dorsal view. (From Furman and Catts, 1982.)

secondary infections. The pigeon fly can bite humans and can be irritating to individuals handling domestic pigeons.

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