HISTORICAL REVIEW The first rhipicephalid to be recognized was the cosmopolitan species Rhipicephalus sanguineus, collected in France and described by Pierre Andre Latreille (1806). His description was brief in the extreme – ‘Sanguineus, punctatus, postice lineolis tribus impressis; dorso antico macula nulla thoracica, distincta.’ Translated from the Latin this means: ‘Blood red, punctate posteriorly with three impressed lines; no distinct thoracic spot anterodorsally’ (M.-L. Penrith, pers. comm., 1997). Latreille placed this tick in the genus Ixodes but Koch (1844) reclassified it as a member of his newly erected genus Rhipicephalus, and at the same time described three new species, R. capensis, R. senegalensis and R. simus. Nearly 30 years later A. Gerstäcker (1873), who studied various arthropods collected by Baron C.C. von der Decken during his travels in East Africa, described R. praetextatus and R. pulchellus. The latter, on account of the ornate scutal pattern of the adults, was originally regarded as a species of Dermacentor.

Towards the end of the 19 th century and early in this century research on ticks rapidly gathered momentum as these parasites became increasingly recognized as important vectors of various animal pathogens. In 1898 an American, C.P. Lounsbury, who had arrived in South Africa 3 years earlier to take up his appointment as Government Entomologist to the Department Department of Agriculture, Cape of Good Hope, turned his attention to ticks and tick-borne diseases. He soon established contact with two outstanding authorities in Europe, L.G. Neumann in Toulouse, France, and G.H.F. Nuttall in Cambridge, England. Neumann, who had already described R. compositus in 1877 and R. evertsi in 1899, based his descriptions of R. appendiculatus and R. nitens on Lounsbury's collections.

The oft-quoted saying ‘a picture is worth a thousand words’ is particularly apt when applied to the immature stages of ticks of the genus Rhipicephalus. Their identification to species level is especially difficult as several of them are so similar in appearance. For this reason we have not attempted to produce keys for their identification. Instead we have included a series of figures in which line drawings of the capitula of nymphs and larvae of morphologically similar species have been grouped. In some contentious cases, but not all, we have been influenced by the morphology of the adults in deciding on our groupings. The diagnostic characters on the capitula of the various species within a group are easily visible in these figures and should assist readers to identify them. In addition brief descriptions of these characters have been given for each group as well as summaries of the geographic distributions of the individual species.

The classification proposed now represents a revision and extension of that initially suggested by Walker (1961). We do not, however, wish to give readers the impression that we regard the present groups as being immutable. Some do appear to be naturally well founded, e.g. the R. evertsi group, comprising R. bursa, R. evertsi and R. glabroscutatum. These three species are not only very much alike morphologically at the immature stage but they are the only species in the genus at present known to have a two-host, rather than a three-host, life cycle. In other cases, though, our placing of individual species in this group or that may be regarded as questionable, e.g. the inclusion of R. armatus in the R. appendiculatus group.

Unless otherwise stated the records in the host/parasite checklist refer to adult ticks. The number in brackets appearing after a tick's name represents the number of collections made from the host species under which it is listed. When a tick's name appears in bold type this indicates that the animal under which it is listed is a preferred host of the adults. Large numbers of domestic cattle., sheep and dogs as well as Indian gerbils and Tolai hares have been examined for ticks within the distribution range of the non-Afrotropical Rhipicephalus species. The numbers of collections from these animals could give a false impression of host preference.

The host groupings under which the tick collections are recorded in the host/parasite checklist follow the same sequence as those in the host record tables accompanying the individual tick species accounts, namely domestic animals, wild animals, birds and humans.

DOMESTIC ANIMALS

Bos indicus/taurus

R. bursa (40)

R. haemaphysaloides (11)

R. pilans (5)

R. pumilio (2)

R. rossicus (8)

R. schulzei (1)

R. turanicus (150 +)

Bubalus bubalisWater buffaloes

R. haemaphysaloides (2)

R. pilans (12)

R. turanicus (3)

Ovis ariesSheep

R. bursa (91)

R. haemaphysaloides (5)

R. pumilio (1)

R. schulzei (1)

R. turanicus (many)

Capra hircusGoats

R. bursa (35, including immatures)

R. haemaphysaloides (8)

R. leporis (1)

R. pumilio (1)

R. rossicus (1)

R. schulzei (1)

R. turanicus (many)

Camelus dromedariusCamels

R. bursa (1)

R. haemaphysaloides (2)

R. pumilio (1)

R. rossicus (1)

R. schulzei (1)

R. turanicus (15)

Equus caballusHorses

R. bursa (10) R. haemaphysaloides (4) R. pilans (8, including immatures)

‘Haba na haba hujaza kibaba’ Little by little fills up the measure! This Swahili proverb encapsulates the contributions made by many people, starting in 1806, towards an understanding of the genus Rhipicephalus an important group of ixodid ticks occurring mainly, but by no means exclusively, in Africa. So far as we know our book represents the first completed attempt to review this knowledge. Almost certainly G.H.F. Nuttall, C. Warburton, W.F. Cooper and L.E. Robinson originally intended to include the genus in their series of monographs on the Ixodoidea but they never managed to do so. The first part, by Nuttall et al. on the family Argasidae, was published in 1908. Thereafter three further parts on individual ixodid genera appeared, by Nuttall & Warburton (1911, 1915) on Ixodes and Haernaphysalis, respectively, and by Robinson (1926) on Amblyomma.

In 1939 F. Zumpt, in the first of a series of papers entitled ‘Vorstudie zu einer Revision der Gattung Rhipicephalus’ noted that he planned to revise the genus in collaboration with Dr W. Minning. However, after publishing a key to the known species within the genus in 1949 he apparently abandoned this idea. In 1960 D.R. Arthur, of King's College, London, produced the fifth volume in the monographic series started by Nuttall and his colleagues in which he dealt with the genera Dermacentor, Anocentor, Cosrniomnia, Boophilus and Margaropus. At the same time he gave notice of his intention to complete the series, including a study of Rhipicephalus and Rhipicentor, but neither this nor his proposed volume on the genus Hyalomma ever materialized.

Ticks are all obligate blood-feeding parasites of terrestrial vertebrates at some stage of their life cycle. Many species are of considerable interest and importance as vectors of a wide variety of pathogens to both humans and animals.

They are members of the phylum Arthropoda, the jointed-legged animals. Although often referred to as insects, whose adults have six legs, they are in fact members of the class Arachnida. This class, whose adults have eight legs, includes spiders and scorpions as well as the order Acari, a large and diverse group to which the ticks and mites belong. Within the Acari the suborder Ixodida encompasses the three families of ticks, the Argasidae, Nuttalliellidae and Ixodidae. The systematics of the Ixodida were reviewed recently by Keirans (1992).

Members of the family Ixodidae, to which the genus Rhipicephalus belongs, are characterized by having a hard sclerotized scutum. This completely covers the dorsal surface of the body in the males but is merely a smaller shield just behind the capitulum in the females and immature stages. The mouthparts of all these ticks are anterior in position; their eyes, when present, are near the lateral margin of the scutum, and their spiracles, which are large, are located behind coxae IV. This combination of characters readily distinguishes ixodid ticks from species in the Nuttalliellidae and the Argasidae. Members of both the latter families lack a hard sclerotized scutum: the main feature characterizing them is the leathery integument that covers their bodies.

Unless otherwise stated the records in the host/parasite checklist refer to adult ticks. The number in brackets appearing after a tick's name represents the number of collections made from the host species under which it is listed. It has been difficult to determine the exact number of records for R. fulvus. Consequently where the name of this tick appears in the host/parasite list it is followed by (+) which indicates that it has been collected from a particular host species.

When a tick's name appears in bold type this indicates that the animal under which it is listed is a preferred host of the adults. However, when the hosts of the immature stages are entirely unrelated to those of the adults the names of these ticks also appear in bold type under the names of the preferred hosts of their immature stages. These ticks are R. follis, R. gertrudae and R. simus. When more collections of their immature stages have been made we feel sure that the same will apply for R. compositus, R. lounsburyi, R. lunulatuSy R. muhsamae, R. neumanni, R. planus, R. praetextatus, R. senegalensis and R. zumpti and perhaps other species too.

Despite the fact that the immature stages of R. pravus, R. sp. near pravus and R. warburtoni are found on hares, on which their adults also occur, they undoubtedly have a preference for elephant shrews. The names of these ticks are also typed in bold under their respective elephant shrew hosts. We are confident that the same will apply for R. punctatus and R. sp. near punctatus once additional collections of their immature stages have been made.

RHIPICEPHALUSAPPENDICULA TUS NEUMANN, 1901

This specific name appendiculatus, from the Latin appendo meaning ‘to hang’, doubtless refers to the appearance of the engorging adults.

Diagnosis

A moderate-sized reddish-brown tick.

Male (Figs 3(a), 4(a) to (c))

Capitulum much longer than broad, length × breadth ranging from 0.69 mm × 0.56 mm to 0.86 mm × 0.71 mm. Basis capituli of smaller males much broader than long but that of larger males only slightly broader than long, with very short obtuse lateral angles at about anterior quarter of its length. Palps short, broad. Conscutum length × breadth ranging from 2.85 mm × 1.85 mm to 3.67 mm × 2.43 mm; large sharp strongly-sclerotized anterior process present on coxae I. In engorged specimens body wall expanded slightly posterolaterally and forming a long slender caudal process posteromedially. Eyes marginal, almost flat, delimited dorsally by a very shallow groove and sometimes one or two large punctations. Cervical fields broad, depressed, with finely-reticulate surfaces. Marginal lines well developed, extending anteriorly nearly to eye level, delimiting one festoon posteriorly. Posteromedian groove long and narrow, posterolateral grooves short and broad, all with finely-reticulate surfaces. Large setiferous punctations present on the scapulae, along the outer margins of the cervical fields and scattered amongst numerous medium-sized punctations medially on the conscutum. Areas surrounding the eyes, adjacent to the marginal lines and anterior to the festoons with fine pinpoint punctations only. In small specimens the pattern of grooves and punctations may be much reduced. Legs increase markedly in size from I to IV. Ventrally spiracles broadly comma shaped, curving gently towards the dorsal surface.

Morphological features used in descriptions of Rhipicephalus spp. and taxonomic and other terms.

Accessory adanal plates Pair of small sclerotized tructures lateral to the adanal plates in males. May be present or absent. Also called accessory plates.

Adanal plates Ventral pair of large

sclerotized structures lateral to the anus in males.

Alloscutum The portion of the body wall in females and immatures posterior to the scutum that expands enormously to accomodate the large volume of blood ingested when these stages feed.

Anterior Towards the front end.

Anterior process Referring to anterior process on coxae I. When seen from the dorsal surface it is a sclerotized anterior projection of these coxae protruding in front of the scapulae as in R. appendiculatus.

Anus Posterior opening of the alimentary tract, situated ventrally and medially, posterior to the last pair of legs.

Article Distinct articulated portion of a jointed appendage.

Basal Closest to the origin or insertion.

Basis capituli Basal portion of the capitulum on which the mouthparts are attached; in the genus Rhipicephalus the basis capituli is hexagonal.

Bifid Deeply cleft, forming two

long spurs. (See coxa).

Capitulum Anterior movable portion of the body which includes the basis capituli, palps, hypostome and chelicerae. The tick's ‘head’.

Caudal process Distinct projection arising posteromedially from the median posterior end of engorged males of many Rhipicephalus species.

Central field Area on the conscutum or scutum between and delimited by the internal cervical margins.

Cervical fields Areas anteriorly on the

conscutum or scutum delimited by the internal and external cervical margins.

RHIPICEPHALUS BURSA CANESTRINI & FANZAGO, 1878

The specific name bursa, from Middle Latin meaning a “pouch” or a “purse made of skin”, refers to the bloated pouch-like appearance of an engorged female of this tick species.

Synonym

?bilenus.

Diagnosis

A large, light brown species.

Male (Figs 230(a), 231(a) to (c)

Capirulum usually slightly broader than long, length × breadth ranging from 0.66 mm × 0.71 mm to 0.88 mm × 0.88 mm. Basis capituli with short acute lateral angles in the anterior third of its length. Palps short, broad. Conscutum narrower anteriorly, broadening posterior to eyes, length × breadth ranging from 1.55 mm × 1.02 mm to 3.34 mm × 2.26 mm; the light tan body wall expanded laterally and posteriorly in engorged specimens. Eyes marginal, slightly bulging, not edged with punctations. Cervical pits deep, then extending as very shallow troughs just posterior to eyes. Punctations numerous, fine, evenly distributed over scutal surface, a few larger punctations in scapular areas. Marginal lines long and narrow, impunctate, delimiting first festoons, and almost reaching eyes. Posteromedian groove narrow, shallow and usually inconspicuous; posterolateral grooves broadly-oval shallow depressions. Ventrally spiracles elongate in anteroposterior axis, each with a short, narrow dorsal prolongation; circum-spiracular setae present. Adanal plates large, pointed anteriorly, broadly rounded posteriorly with cusps or pointed prominences on their internal margins; accessory adanal plates absent or present as very small, light-brown, sclerotized points.