HOSTS Cattle (All references). Rarely giant eland and domestic donkey (Sudan records above). In America, other domestic animals, deer, and buffalo have been reported as infrequent hosts (Cooley 1946). BIOLOGY Life Cycle Like other boophilids, the Texas fever tick is a single host parasite. Its life cycle has not been studied in Africa, where it is not known to occur under cold conditions. After dropping from the host, the female commences oviposition in about three or four days but after twenty to forty days in winter (southern United States). The oviposition period ranges from eight or nine days in summer to 42 days in winter. The number of eggs average 1911, with a maximum of 3806. With abundant moisture, eggs may hatch in as little as from 17 to 21 days, but up to 44 days is more common. Winter incubation may require between five and six months. A few hours after hatching, larvae collect in masses at the tip of grass, and may remain alive from 49 to 159 days awaiting a host. Once an animal is found larvae preferentially attach to the legs, belly, or dewlap, but if numerous they are found everywhere on the body. The larval nymphal molt occurs seven to twelve days later and nymphs molt to adults five to ten days afterwards. Females feed for from four to fourteen days, during which time they mate, and then drop to the ground, oviposit, and die. These data are extracted from the very com plete work of Hunter and Hooker (1907) in the United States. Ecology Most African specimens are from collections containing more mmerous B. decoloratus, with the exception that during the rainy season the numbers of B. annulatus have in some instances exceeded those of B. decoloratus. In Cameroons (Rageau 1953B), this tick is less common than B. decoloratus but both species are found together. Our first suspicion, that this might be a species ac climated to humid West Africa, is negated by finding it in Sudan localities with long, severely hot, dry seasons. The Texas fever tick occurs in the Sudan in areas with from 800 mm. to 1500 mm. annual rainfall. The ecology of B. annulatus is unstudied in Africa and the results of research on this subject are awaited with considerable interest. In North and Central America, B. annulatus is entirely a tropical and subtropical tick that dies out when introduced into the northern states. DISEASE RELATIONS Unstudied in Africa. B. anmulatus in America is the famed vector of Texas fever of cattle (Babesia bigemina). REMARKS Minning (1934) considered West African populations to differ from New World B. annulatus and called them B. congolensis. Nu merous B. anmulatus specimens from the United States and Central America have been examined in collections of British Museum (Natural History), Rocky Mountain Laboratory, Museum of Comparative Zoology, as well as Louisiana material kindly presented by Dr. F. C. Bishopp from United States Department of Agriculture collections. None of these can be distinguished from African B. congolensisTM. The chief characters presented for differentiating males are the pointed outer spur of coxa I of B. congolensis" and the blunt outer spur of coxa I of B. annulatus. In a few African specimens this spur is blunt, in many American specimens pointed. The American specimens in the Nuttall collections at British Museum (Natural History) are mostly blunt-spurred with few pointed spur specimens, but those at the Rocky Mountain Laboratory in Montana are almost entirely pointed spurred. Specimens from Louisiana in the present collection have pointed spurs. It is evident, therefore, that this character is a variable one with no diagnostic significance as to species. The shape of the eyes of African and American specimens is similar. Examination of other so called differentiating characters has also failed to reveal differences. Similarly, no points of differentiation may be detected be tween female specimens from Africa and America. The chief diagnostic characters proposed for these, arching of the eyes and shape of the distal margin of the third palpal segment, appear similar, as are all other morphological features of specimens from both continents. Minning stated that the scutum of American B. annulatus bears hairs and the scutum of B. congolensis" does not. Several African specimens with scutal hairs and some American B. annulatus without scutal hairs are available, though they may have been rubbed off the latter. Theiler (1943B) has already observed that the relation of the position of the eye to scutal margin in Boophilus ticks is subject to variation according to degree of engorgement. As already stated (page 296) no differences between length/width ratio of the female scutum can be determined in field collected material of each species. As stated above, it appears that there are no constant differences between American and African populations of B. annu latus. Likewise, it is impossible to differentiate between American and African populations of B. annulatus, and specimens col lected in North Africa, Southern Europe, and the Near East, which Minning (loc. cit.) referred to as B. schulzei and as B. calcara tus subspp. In their classic work on this parasite in America, Hunter and Hooker (1907) open by observing "It is safe to state that no more important problem than the eradication of (B. annulatus) ...... confronts the farmers of any country. Not only the cattle raising industry but the whole economic condi tion of a large section of country is affected". The Texas fever tick is now completely eradicated from the United States except for periodic introductions from Mexico, where it still exists. At the turn of the century it ranged through Mexico and the sixteen southern states of the United States from the Atlantic to the Pacific. The history-making discovery by Smith and Kilbourne (1893) that Babesia bigemina is the cause of Texas fever of cattle was followed by their finding that this tick is the vector. The life history and morphology of the tick have been reported handsomely by Curtice (1892), Salmon and Stiles (1902), Hunter and Hooker (1907), and Hooker, Bishopp, and Wood (1912). The latter report contains a useful summary of the antecedent literature. IDENTIFICATION Males are easily identified in the African fauna. They have no caudal appendage on the posterior body margin and the inner margin of the adanal shields does not project posteriorly as a spine. Palpal segment I is without a ventral bristle bearing protuberance. The hypostome formula is 4/4 and the denticles are noticeably finer than those of B. decoloratus. In size, males are about the same as those of B. decoloratus. Females are usually readily separated from B. decoloratus by absence of a deep gap between the inner and outer spurs of coxa I. A shallow concave emargination replaces this gap. There is no bristle bearing protuberance on the internal ventral margin of palpal segment I; this margin is fairly elongate and mildly con cave. The scutal margins anterior of the eyes are usually straight and parallel. The scutum is definitely longer than wide. The hypostome formula is as for the male. The color of this spe cies is usually paler than that of B. decoloratus. |