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I 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. 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 copula
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 (19130,1916). The African representatives of this genus are re viewed 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 spe cies 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 cavipalpus and I. rasus are known to bite man. In southern Africa, I. rubicundus 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 fre quently quoted misstatement (Theiler, correspondence).

KEY TO SUDAN SPECIES OF IXODES

MALES*

1. Legs longer than body. (From bat habitats)....

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

....I. VESPERTILIONIS Figures 232 and 233

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

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Figures 212 and 213, ♂, dorsal and ventral views Figures 214 and 215, o, dorsal and ventral views

SPECIAL MORPHOLOGICAL FEATURES, IXODES TICKS

PLATE LXI

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