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It has been attempted herein to indicate present and previous nomenclatorial concepts of these species as clearly as possible, especially for experimental workers and reviewers. Non_taxonomists, who consider themselves "practical workers', will undoubtedly be annoyed by the remaining confusion. The end is now in sight, and within a very few years will undoubtedly be reached. A little more patience will be rewarded by better understanding of what has been an especially difficult complex of variable species in previously poorly explored parts of the world.
HYALOMMA DISTRIBUTION IN AFRICA
Two species, H. truncatum and H. rufipes, are common in drier areas throughout the Ethiopian Faunal Region (Figure 1). Two others, H. albi parmatum and H. impressum, are restricted to equa torial regions of Africa; these four species appear to have e volved in Africa from Near Eastern stock. Only H. rufipes ex tends beyond the confines of the Ethiopian Region. Two other species (H. detritum and H. marginatum) range into North Africa from the Near East and have tenuous, scattered footholds in the transitional zones just south of the great deserts along the northern periphery of the Ethiopian Region. Another Near Eastern species, H. impeltatum, appears to be extending its range a little more aggressively into East and West Africa. The last species known from continental Africa, H. turanicum, has established ita self in the South African Karroo after having been introduced on sheep from the Near or Middle East.
In East Africa, the arid lowlands along the Red Sea and the Indian Ocean carry a number of Near Eastern and North African species southwards into the Somalilands and parts of Kenya to wards and even slightly south of the equator. For instance, H. dromedarii is known from the coastal lowlands of Kenya (Walker, unpublished) and H. impeltatum occurs in scattered foci in Kenya and Tanganyika.
There is little question that other species do exist in nature but their identity can be established only by breeding experiments. The presence of a possibly undescribed species similar to H. drome
darii in the French Somaliland fauna has also been noted (Hoogstraal 1953D).
Note the following incorrect Ethiopian Region records:
H. marginatum (= H. savignyi), reported by Rousselot (1948) from French West Africă, was not subsequently confirmed (Rousselot 1953B).
H. detritum reported from French Cameroons (Rageau 1951) was subsequently (1953) assigned to H. truncatum (= H. transiens by the same author.
References to "H. savignyi" from Portugese Guinea (Tendeiro 1949,19520) actually apply to H. truncatum.
In northern and central Sudan, eight species are established though seldom in a continuous range. Of these, only four are com mon. In most Near Eastern and North African areas about the same proportion of common and rare species occur. Yet with even so few species among which to choose the student frequently encounters difficulty in positive identification of all material in most large collections. Some specimens are so variable and intermediate that they defy assignment to a definite species. Unfortunately, previous workers have not provided pertinent details over extremes of variation among species that they have reared. Attempts to properly identify Sudan material for this report have necessitated So much study of material from other parts of the world that pub. lication has been long delayed.
With regard to the paucity of specimens of some species col lected in northern Sudan, it should be emphasized, from our ex perience with vertebrate and invertebrate animals in arid and semiarid areas of Africa, Arabia, and the Near East, that not infrequently small relict populations of animals are found in explicably surviving in barely marginal habitats.
This appears to be true of H. detritum, H. marginatum, H. truncatum, and H. impressum in northern Sudan.
The northcentral areas of the Sudan, by reason of their proximity and similarity to the Mediterranean subregion and their tenuous routes of entry from Arabia, West Africa, and via
the Nile, are inhabited by more species of Hyalomma ticks than apparently any other area of the Ethiopian Faunal Region. The fact that some of these species appear to be represented in the Sudan only by small populations, either as a result of chance introduction or as survival or relicts, has been noted above.
The Asiatic species that do not reach the Sudan are H. hussaini of India (page 520), H. schulzei, an Iranian camel parasite that reaches the Sinai Peninsula between Asia and Africa (page 525), H. aegyptium, the tortoise parasite that extends from southern Russia westward through much of the Mediterranean basin (page 514), and H. turanicum of southern Russia and Iran that has been introduced into the South African Karroo (page 528). As stated above, the original center of distribution of hyalommas appears to have been in southern Russia or Iran.
Delpy and Adler and Feldman Muhsam have provided fow de tails about the geographical source and range of species that they treat, and there is still considerable question in the minds of specialists and reviewers as to the distribution of Hyalomma species. This section has therefore been given special attention in the following text. Synonyms, listed by country of origin of specimen material whenever it can be determined, are based on Delpy's (1949B) lists, which give every evidence of being carefully and judiciously assembled. These references do not include the entire literature, except I trust for Africa, but are furnished for what they are worth in elucidating the distribution of Hyalomma species and indicating the major stu dies of each species in different parts of the world.
HOSTS AND BIOLOGY
Biological data for Hyalomma ticks derive chiefly from veterinarians' observations on those infesting domestic animals and on laboratory experiments. From field work and from a few other sources we have gained a somewhat different impression of Hyalomma biology, especially relating to host preferences of the immature stages. In this respect, special attention is called to the HOSTS and BIOLOGY sections in the following text, especially for H. excavatum. The natural life cycle of Hyalomma
ticks may be altered by the size, members, and density of available hosts. Further research on this subject is strongly indicated.
In the introduction to this section it has been stressed that many Hyalomma populations survive in inclement environments and are greatly affected by extremes in temperature, humidity, and condition of host nourishment, as well as by the wide wandering of their hosts over thinly populated, inhospitable xeric areas.
Much more collecting, observing, and careful identification is necessary before the ecology of most species in this genus can be adequately determined. The value of innumerable published reports on the biology of the genus is vitiated by the inaccuracies in identification,
Extraordinary survival factors play a large part in permitting these ticks to exist and even thrive where few or none others live.
The life cycle of byalommas may be greatly lengthened in un favorable climatic conditions, or shortened under optimum condi. tions. Nuttall (1915) kept adult specimens alive without food for approximately two years and observed copulation and feeding after this period of starvation. Nuttall (1920) also found the capacity for regeneration of lost appendages and injured mouth parts to be greater in Hyalomma ticks than in most others. A certain amount of hybridization is possible though curiously mis formed individuals may result; these and other greatly mi sformed specimens that have still survived are reviewed by Pervomaisky (1950B, 1954).
Special attention is called to the discussion below of the two_host, summer-feeding H. detritum, and its biological race H. scupense which is a single host, winter-feeding form with Bligat morphological differences in most of its range (page
Adult Hyalomma ticks, except H. aegyptium, are today chief. ly parasites of domestic animals wherever they are found, and, as such, are of considerable economic importance. Hyalommas
appear to be unusually efficient vectors of a variety of disease causing organisms. In their immature stages, they often feed on birds, rodents, and hares that are important reservoirs of patho. gens, especially viruses and rickettsiae.
Few ticks have been incriminated as reservoirs and vectors of pathogenic viruses, but several species of hyalommas are known to be hosts and vectors of the viruses causing several distinctive acute infectious hemorrhagic fevers of human beings in the Soviet Union. Unpublished studies by Daubney (conversation) indicate that one of these same species may transmit in nature the virus causing a Near Eastern encephalomyelitis of equines. These same tick species occur in North Africa and northern Sudan. Other species cause paralysis of men and animals, apparently as a result of toxins injected into the host while the tick is feeding. The association of Hyalomma ticks with a number of other human and veterinary diseases is noted in the following text.
Many Hyalomma species, in our experience, attach readily to man and feed on him. The "cursorial ticks of North African and Arabian deserts, as first described by Mann (1915), are several species of hyalommas that come rushing from beneath every shrub when persons or animals stop nearby. These are almost invariably unfed adults, of uniform size, shape, color and general appearance, that have molted from the nymphal stage in rodent burrows beneath shrubs. Although few of these highly agitated young adults actual ly attach to man, some do.
Confusion in nomenclature has limited the value of many ear. lier studies on biology and disease transmission in this group, for it is often impossible to be certain which species the writer used in his work. Considerable study on this genus has been and is being done in Russia, and it is frequently difficult for reviewers to determine exactly the species being reported and to satisfactorily evaluate the reports.
In addition, it should be indicated that the range of Hyalomma ticks covers, in large part, a vastly undeveloped part of the world in which little serious scientific research has been accomplished. Before many years have elapsed, enough evidence probably will have been presented to indicate that Hyalomma ticks are economically among the most important of animal ectoparasites to be found anywhere in the world.