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|XODES
INTRODUCTION

Ixodes ticks are highly specialized in their habits. They frequently parasitize small or seldom-examined hosts and are so small themselves that they are easily overlooked. Of some twentyfive species in Africa, six occur in the Sudan. Only sixteen specimens of the whole genus have been collected in the Sudan, all but three of these by the writer. This paucity of material is in striking contrast to Kenya, Cameroons, and Nigeria, where careful collecting is fairly productive for several species.

Phylogenetically, Ixodes ticks occupy a solitary position as a unique, highly specialized branch from proixodoidea stock. Several exceptional morphological characters may be seen easily by comparison of Ixodes illustrations with those of other genera. The absence of eyes in this genus is believed by some to be a primitive character and the sexual dimorphism of the mouthparts is unparalleled in other ixodid ticks.

Intraspecific variation in the African Ixodes fauna is still poorly understood because only small amounts of material from many localities are available and probably also because these variations do not conform to those typically expected in ticks. Dr. D. R. Arthur of King's College, University of London, is presently undertaking an exhaustive study of this subject.

Biologically, ticks of this genus offer a wide field for research; their habits differ from all others. To elucidate this, Nuttall (1911A) erected the following biological criteria for Ixodes ticks:

I. Species in which both male and female occur on the host.

(a) Species in which the sexes are found in copule
on the host (usually on wandering hosts).

(b) Species in which the sexes are found near each

other on the host (on either wandering or fixed
habitat hosts).

II. Species in which only females are found on the hosts,
and in which males may or may not be known.

Although the males of species confined to the Ethiopian Faunal Region (except Ixodes nairobiensis Nuttall, 1916 and I hoogstraali Arthur, 1955) are known, their habits are still obscure.

The genus Ixodes has been reviewed by Nuttall and Warburton (1911), to which important additions have been made by Nuttall (1913C, 1916). The African representatives of this genus are reviewed by Arthur (ms.), who also proposes a number of new species.

Careful examination of rodents and other small animals, and of dogs and other domestic animals will probably reveal other species in the Sudan, especially on the west bank of Equatoria Province. Search in rodent nests, animal lairs, and bat caves and retreats should prove fruitful.

No African Ixodes has been reported to transmit human diseases, but at least Ixodes cavipal and I. rasus are known to bite man. In southern Africa, Trubicundus is an important cause of tick paralysis of sheep. "I. pilosus, to which this condition is most commonly attributed in literature, plays no known rôle in this affliction; early misidentification was the cause of this frequently quoted misstatement (Theiler, correspondence).

KEY TO SUDAN SPECIES OF DXODES
MALES*

habitats). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .I. VESPERTILIONIS

l. Legs : than body. (From bat Figures

Legs not longer than body. (Not from bats)....................... . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

*The males of I. nairobiensis and of I. S • simplex are not known.

Palpal base forming a lateral projection from basis capituli, palpi converging anteriorly. Scutum

sharply narrowed posteriorly.

(Shrew parasite, uncommonly on other insectivores and rodents)...................I. ALLUAUDI

Figures 339 and 570

Palpi normal, arising from anterior of basis capituli and parallel. Scutum gradually or bluntly rounded posteriorly. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Anal grooves united. . . . . . . . . . . . . . . . . . . . . . . . . . .I. RASUS SUBSP. Figures 222 and 223

Anal grooves not united posteriorly. . . . . . . . . . . . . . . . . . . . . . . . .4

Scutum with faint, shallow puncta

tions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .I. CAVIPALPUS Figures 2TETERTZT7

Scutum with numerous large, uneven punctations. (Monkey parasite)................I. SCHILLINGSI Figures 225 ERT227

FEMALES

Legs longer than body. (Bat :...' - - - - - . . . . . . . . . . . . . .I. WESPERTILIONIS Figures 237 ERT2:5

Legs not longer than body. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Palpi arising laterally from basis capituli. Scutum abruptly converging posteriorly, with few medium punctations; cervical grooves lacking; lateral grooves fine. . . . . . . . . . . . . . . . . . . . .I. ALLUAUD! Figure 5T

Palpi normal, arising from anterior margin of basis capituli...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

4.

Anal grooves horseshoe shaped or elliptical, not united posteriorly. . . . . . . . . . . . . . . . . . . . . . . . . .4

Anal grooves either united posteriorly or parallel or divergent posteriorly. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Scutum at least l.5 times as long

as wide; punctations few and fine;

lateral ridges distinct. . . . . . . . . . . . . . . . . . . . . . .I. NAIROBIENSIS Figures 22U and 22I

Scutum only slightly longer than wide; punctations large, distinct, deep; lateral ridges absent. . . . . . . . . . . . . . . . . . . .I. SCHILLINGSI

Figures 223 and 229

Anal groove closed posteriorly. . . . . . . . . . . . . . . .I. RASUS SUBSR.
Figures 227 and 225

Anal grooves not closed poste

riorly......................................................6

Anal grooves short, divergent pos-
teriorly. Basis capituli without
cornua or auriculae. Scutal punc-
tations fine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .I. S. SIMPLEX

Figures 230 and 231

Anal grooves long, parallel poste-
riorly. Basis capituli with cornua;
auriculae lacking. Scutal puncta-
tions large. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .I. CAVIPALPUS

Figures 218 and 219

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Figures 212 and 213, d, dorsal and ventral views Figures 214 and 215, Q, dorsal and ventral views

SPECIAL MORPHOLOGICAL FEATURES, IXODESTICKS

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