February, '15] 



COOLEY: SPOTTED FEVER TICK 



51 



host. Thus, it is apparent that a part of each brood may prolong Hfe 

 in this manner, thus making the cycle three years instead of two. 



Studies now under way indicate the possibility of a still further length- 

 ening of the life-C3^cle. 



With these facts in view it is apparent that with ver}^ thorough work 

 done in a given district, resulting in preventing any females from 

 engorging and laying eggs for two consecutive years, there still may 

 be adults present in the third season, or if only incomplete work has 

 been done for three or four years even, there still will be adults present in 

 later years. 



Control 



The foregoing facts regarding the host relationships have indicated 

 a practical plan of controlling the tick in the valley. It is evident 

 since engorgement is necessary before egg-laying, that if no adults are 

 allowed to engorge the species cannot continue. This point is believed 

 to be of much importance and has led to the adoption of dipping of 

 domestic animals as a main dependence in the program. There are 

 two limitations to this method which we recognize, but these we think 

 are not serious. One is the fact that some adults may engorge on wild 

 animals, such as the coyote, bear and deer. These animals are not 

 abundant in the valley and we believe that the small number of en- 

 gorged adults which they drop may be neglected. The practicability 

 of getting all owners of stock to dip under the conditions found in the 

 valley is more serious. If spotted fever affected the animals instead of 

 man, it would apparently be less difficult to secure the owners' coopera- 

 tion. A shght danger of injury to the animals is greatly magnified 

 and the residents Tsdsh to see some other method of tick destruction 

 developed. The arsenical dip in use has been found to be effective and 

 we believe that as the farmers gain confidence dipping will be more 

 generally adopted. However, notwithstanding this limitation many 

 animals are already being dipped and thereby freed of ticks. 



Rodent destruction naturally suggests itself as a method of control. 

 Ground squirrels are very abundant and the property owners are quite 

 willing that they should be killed off. Some work in this direction has 

 been done and there can be no doubt that it is of value in the destruc- 

 tion of ticks as we have found that this rodent, far more than any other, 

 is responsible for the feeding of larvae and nymph ticks. The cost of this 

 work under the conditions that prevail in the region affected is such as 

 to raise a serious obstacle. This might, however, be overcome if the 

 killing of this squirrel alone would be a sufficient means of getting rid 

 of the tick. It is apparent that since the early stages of the tick feed 

 also on other rodents, other means of tick killing will eventually be 

 needed. It is not yet clear that with ground squirrels eliminated there 



