I XODES 



INTRCDUCTION 



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 twenty- 

 five 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. 



Phylo genetic ally, Ixodes ticks occupy a solitary position as 

 a xmique, highly specialized branch from proixodoidea stock. Sev- 

 eral exceptional morphological characters may be seen easily by 

 comparison of Ixodes illustrations vrith 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 raouthparts 

 is unparalleled in other ixodid ticks. 



Intraspecific variation in the African Ixodes fauna is still 

 poorly understood because only small araoimts 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. 

 Arthvir of King's College, University of London, is presently linder- 

 taking an exhaustive stiidy of this subject. 



Biologically, ticks of this genus offer a wide field for re- 

 search; their habits differ from all others. To el\icidate 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). 



- 535 - 



