Ecology "It would appear that R. pravus shows a preference for bush veld or dry parklands (in South Africa, and) avoids open grasslands or more humid parklands. It occurs in areas with seasonal rainfall alternating with fairly long dry periods, and with a rainfall above ten inches and below 25 inches. It appears to be relatively frostresistant, being established in areas with over 90 days of frost per annum." Theiler and Robinson (1953B)_7. These conditions are generally also true for the Sudan, except that R. pravus is not uncommon in the open grasslands and sparsely treed savannah of Torit District, where the annual rainfall varies between 40 and 50 inches. However, it is much more common in the more arid grasslands and savannahs of Eastern District. It is rare or absent in Juba and other districts to the west of Torit, which have higher rainfall, denser savannahs, and forests. Torit and Eastern Districts both have long dry seasons. The apparent absence of R. pravus north of Torit and of Eastern Districts may be due to paucity of collections or lack of population pressure on the north ern periphery of its range. Highland records from goats at Katire and Nagichot may rep resent introduced individuals, if not, they are difficult to explain from these humid, forested areas. In Central Africa and Western Province of Nigeria, R. pravus may invade high rainfall areas (average over 60 inches per annum) as suggested by Walker (1956). Rosevear (1953) indicates that in areas with high average rainfall but long dry seasons, vegetation may be of a more xeric type than in areas with a lower rainfall but higher dry season humidity. Such factors may explain the rather implausible range of a xerophilic tick like R. pravus into certain outlying high rainfall average areas. Cattle brought into these areas for slaughter may also influence the picture. Lewis, Piercy, and Wiley (1946) found that in Kenya, R. appendiculatus and R. pravus occur together in some areas presumably marginal for both species (i.e.: Karati Forest, Taveta District, northwest section of Narok District in the Masai Reserve, southern part of Ukamba Reserve, Kapenguria area of Turkana Province, and between the Athi and Tiva Rivers; also several areas of Uganda and Tanganyika). However, only R. pravus occurs in drier areas, i.e.: Loita Plains in the Masai Reserve where the game of the open plains, savannah, and forest are favorite hosts and cattle and sheep are also infested. Native stock and wild game in the dry scrub country between the Tiva River and Somalia are heavily infested. R. pravus is also extensively distributed in certain desert areas of Northern Province and extends into Karamoja District of Uganda and into Tanganyika. Since the above remarks were written, Wilson's (1953) interesting and important contribution, concerning the R. pravus (R. neavi) - A. gemma association in the drier parts of East Africa and the R. appendiculatus - A. variegatum association in the more humid areas of East and Central Africa, became available. The latter association is discussed herein under A. variegatum (page 274). R. pravus and A. gemma are invar Iably associated where rainfall very rarely exceeds 20 to 25 inches per annum. A. gemma is not known from the Sudan; the Sudan distribution of R. pravus is discussed above 7. These two species range from the dry Karamoja District of north ern Uganda and the arid Northern Frontier of Kenya in the dry belt of country between a line drawn east of Mt. Kenya and the Machakos highlands and west of the humid coastal belt of Kenya. A. lepidum is also common in this area and R. e. evertsi H. truncatum, and H. rufipes occur in smaller numbers in Kara moja. In Northern Frontier, Rhipicephalus pulchellus is also present in small numbers but it becomes very common in the dry eastern belt of Kenya, where smaller numbers of a great variety of ticks were found in association with the two species under discussion (R. simus simus, R. mühlensi, R. humeralis, etc.). Karamoja soils (like those of much of the southern Sudan) are dark grey or dark brown calcareous clays (previously fre quently called "black" or "cracking cotton soil") which become exceedingly sticky when wet and form large, deep cracks when dry. Vegetation is either open marshy grassland or grassland associated with Acacia and Combretum woodlands. In this area there is a long, intense dry period but in the shorter rainy season fifteen to twenty inches of rain falls per annum though once in every twenty years there is a rainfall of over 25 inches. DISEASE RELATIONS Man: Note the several records of R. pravus attacking man in the Sudan. Domestic animals: There is a suspicion that the "R. bursa" which Daubney and Hudson (1934) considered as a possible vector of Nairobi sheep diseases is actually R. pravus. It may, however, have been R. kochi or R. hurti. R. pravus is an efficient laboratory vector of East Coast fever (Theileria parva) but is not known to act in this capacity in nature, possibly because its immature stages do not feed on larger domestic animals. REMARKS For synonymy of this species, see Theiler and Robinson (1953B, p. 134) and Walker (1956), who have also redescribed the adult stages and described the immature stages. Santos Dias (1952E) has described a gynandromorph of R pravus (as R. neavi). IDENTIFICATION Male: The combination of a large, triangular, dorsal projection of coxa I and of slightly convex eyes bordered by at least a furrow or usually by a completely encircling groove, readily distinguishes this from other species. In South Africa, the convexity of the eye seems to be more variable and the en circling furrow is confined to the anterior margin of the eye. No Sudanese specimens without convex, mostly fully encircled eyes have been seen. The moderately numerous, fine and medium size punctations, and the shape of the adanal shields (Figure 286) further distinguish males, as does the narrow posteromedian groove and the short but wider posterolateral grooves. All Sudanese specimens are small (about 3.5 mm. long and 2.1 mm. wide) and shiny brown. Females: This sex can be readily distinguished by the ab sence of lateral grooves which are replaced by a row of puncta tions, and by the conspicuous, convex (but not hemispherical) eyes, with a groove sometimes entirely but more usually only anteriorly bounding the eye. Scutal punctations are moderate in number, medium size with scattered larger punctations; the scutal outline is slightly longer than wide and has a strongly converging posterior margin. The body and legs are brown. |