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ticks may be altered by the size, numbers, 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 alomma populations survive in inclement environments and are grea y 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.
ktraordinary survival factors play a large part in permitting these ticks to exist a.nd even thrive where few or none others live.
The life cycle of hyaloxmnas may be greatly lengthened in un.. favorable climatic conditions, or shortened under optimum conditions. 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 H alomma ticks than in most others. A certain amount of hybridIzati' on is possible though curiously misformed individuals may result; these and other greatly misformed specimens that have still survived are reviewed by Pervomaisky (195oB,19s1.).
Special attention is called to the discussion below of the
Adult H alomma ticks, except H. as ium, are today chief. 1y parasites of domestic animals wherever ey are found, and, as such, are of considerable economic importance. Hyalommas
appear to be unusually efficient vectors of a variety of diseasecausing organisms. In their immature stages, they often feed on birds, rodents, and hares that are important reservoirs of pathogens, 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 huan 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 Unpublished studies by Daubney (conversation) indicate that one of these same species may transmit in nature the virus causing a Near Eastern encephalomyelitis of equines.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 man and animals, apparently as a result of toxins injected into the host while the tick is feeding. The association of H alomma ticks with a nuber of other huan and veterinary diseases is noted in the following text.
Many g§alomma species, in our eperience, attach readily to man and fa on m. The "cursorial ticks“ of North African and
Arabian deserts, as first described by Mann (1915), are several species of hyalomas 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 man 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 H alomma 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 H alomma ticks are economically among the most important of ani ec parasites to be found any. where in the world.
Use of the following key should never be attempted without reference to the section on identification for each species men. tioned in the text. In the identification section, an attempt has been made to present lucidly all important characters of typical specimens and to indicate the range of variability seen in each species. I am most grateful to Mr. Makram N. Kaiser, Chief Technician in the Department of Medical Zoology at U.S. Naval Medical Research Unit, who has served as a "sounding board" and has given invaluable assistance in grouping the very large numbers of specimens that have been studied and often restudied for this section. Special acknowledgement should also be made of the services of Dr. L. P. Delpy, who initially iden. tified many of our early collections of H alomma an of Mr. Glen Kohls who has spent several days con¥errlng over specimens
in the Schulze collection, now deposited in the Rocky Mountain Laboratory at Hamilton, Montana.
Persons attempting to identify fie1d_collected material of H alomma should recognize that a certain proportion of spec. imens In many series will defy final determination of species. These had best be called "Hyalomma species" and sent to a capable
specialist in the group or pu as de for further study as addi. tional information becomes available.
Center of subanal shields character.
Center of subanal shields character.
Medimn size ticks (scutum about 3.8
x 3.0 mm.). Lateral grooves extending
on cattle in central Provinces). . . . . . . . . . . . . . .!_-I. D4PELTATUM Figures 1'70 and 1'71
Lar e ticks (scutum about 4.5 x 3.2
rmn. . Lateral grooves limited to
posterior third of scutum. Scutum
with few lar e , scattered, irregular
punctations sometimes also with
small ones). (Common where camels
Figure? 152 and 133
*In _I_!. excavatum, and sometimes in other species that have en. gorged on large animals such as camels, and have considerably stretched their integument, the subanal shields may be laterally
Such excavatum specimens would appear to be H.
dromedarii, exceph for smaller size, fewer and smaller shutal punchafions, and differences in the caudal area of the scutum. See also identification of H. imfiltatum for superficial varia. tion among unfed males, which may cause them to be suggestive
of H. marginatum.
Lateral grooves not extending beyond
the posterior third of the scutum.
Scutum with few punctations except
in the caudal area which is depressed
between two lateral ridges and some.
times very shagreened. Small ticks,
often frail, maximum overall length
usually less than 5 m. (Fairly
common on cattle and especially on
horses in central Provinces- also
occurs in Northern Province).......................H. EXLCAVATUM
Lateral grooves extending beyond the
midlength of the scutum (may be obs.
cured in.very heavily punctate spe.
cies; examine by oblique orientation).........................4
Scutum smooth, bright*, with very few,
large, shallow, scattered, punctations;
posteromedian and paramedian grooves
well marked. Legs usually not ringed.
(In northcentral Provinces; rare)................... . IETRITUM
H Figures'I58 and 159
*Do not confuse this with H. truncatum that has a smooth, shiny scutum but also dense puntations in a rectangular field poste. riorly.