218 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 6 



it appears certain that the disease is usually contracted in the night- 

 time. Ticks may bite both day and night. They are not excluded 

 because the infective individuals or adult females are large enough 

 and evident enough to be seen and felt and thus avoided during the 

 daytime or while man is awake, but can bite him for hours at a time 

 while he is asleep. It is to be noted further that verruga may be 

 contracted during various seasons of the year, but its principal season 

 of prevalence is during March and April, about the close of the warm 

 rainy season. This is the time of the year when the adult ticks are 

 washed down the steep slopes by the rains and are thus to be found 

 in the greatest number looking for hosts on which to engorge. 



The fact that the verruga districts both descend lower and ascend 

 higher in Ancachs Department than in Lima Department would 

 indicate that neither the transmitter nor the reservoir of verruga is 

 specially restricted or conformable to any particular range of altitude, 

 but rather to the existence of certain conditions, and that both are 

 equally at home in quite low as well as rather high altitudes. Certain 

 ticks have an extensive altitudinal range, as the Rocky Mountain 

 spotted-fever tick, while it is practically certain that no bloodsucking 

 hexapods of the Andean region have such an extended vertical distri- 

 bution as is covered by the verruga districts. The local differences 

 in vertical range of the disease above pointed out would indicate 

 dependence of the reservoir fauna or of the transmitter on local condi- 

 tions not connected with altitude, as just hinted, perhaps primarily 

 on the existence of uncultivated areas within each of the separated 

 foci of infection. The eggs of ticks are very susceptible to the direct 

 rays of the hot sun, and this may well account for the absence of ver- 

 ruga in certain districts under cultivation but within the altitudinal 

 range of the disease. No such explanation can be applied in the 

 case of hexapod bloodsuckers occurring in the region in question. 



In March and April, 1912, verruga appeared at Matucana with 

 Considerable force, this locality being outside and above the infected 

 Rimac district as theretofore known and at an altitude of about 7,800 

 feet. In certain 3'ears there are greater or less extensions of the 

 disease, which seems usually to contract again the following year to 

 its previous bounds. These fluctuations in range are probably only 

 partially if at all dependent on periodic extension and contraction 

 of the native reservoir fauna, carrying with it the transmitter as it 

 advances or recedes and are more likely to be dependent on fluctuat- 

 ing extensions of the transmitter due to some unusual cause. As the 

 Matucana extension took place near the end of the rainy season, it is 

 likely that unusually heavy rains had washed the tick transmitters 

 down the steep slopes of side canyons in the vicinity. 



