144 Acarology 



Discussion: Ticks in general, and ixodids in particular, are perhaps 

 the best known of any of the Acarina. That this is so is not surprising 

 since they are also the largest of the Acarina, parasites of man and his 

 domestic animals as well as wild animals, and the vectors of many 

 serious diseases. Despite the broad knowledge of ticks there is con- 

 siderable disagreement among specialists on the generic names to be 

 applied to them. The arrangement of the genera listed here is taken 

 largely from Vitzthum 1941, who in turn has followed Schulze. Other 

 specialists prefer to reduce many of Schulze's names to synonymy. 



The life cycle of ixodids is fairly simple. The female deposits a large 

 egg-mass on the ground. Six-legged larvae hatch from the eggs. The 

 larvae then feed on a suitable host. After the larvae become engorged 

 with blood they molt and become nymphs. The nymphs have eight 

 legs and are similar in appearance to the adult female. However, they 

 are smaller and lack a genital opening. Nymphs engorge and molt to 

 produce adult males and females. Both males and females feed. The 

 male is encased in a fairly nonelastic integument and so does not in- 

 crease greatly in size after feeding. The female, on the other hand, 

 swells greatly during engorgement. After copulation and engorgement 

 the female is ready for oviposition. 



This general life cycle exhibits many modifications in different de- 

 tails. The majority of ixodids usually parasitize different hosts in the 

 immature and mature stages. For example, Dermacentor venustus Neu- 

 mann i= D. andersoni Stiles) has been reported in the larval and 

 nymphal stages from small mammals, while as an adult it has been 

 taken from sheep, goats, man, etc. D. venustus drops to the ground 

 in order to molt or lay eggs, so that each tick must find at least three 

 individual hosts if it is to complete its life cycle. Boophilus annulatus 

 (Say) on the other hand attaches itself to cattle in the larval stage and 

 does not leave its host until it is ready to lay its eggs. Nuttall 1911 

 indicates that Ixodes rincinus (Linnaeus) can complete its life cycle 

 in as little as one hundred and seventy days, but that under unfavor- 

 able conditions it may take two or three years. 



Ixodids are of great economic and medical importance. Heavy in- 

 festation with ixodid ticks can cause anemia in domestic animals. 

 Several noxious diseases are carried to animals by ticks such as Texas 

 cattle fever to bovines by Boophilus annulatus (Say). Ixodids may 

 cause paralysis in man by their bites and they also have been incrimi- 

 nated in transmitting the following diseases to man: Rocky Mountain 

 and other spotted fevers of the Americas, fievre boutonneuse, Kenya 



