LIFE HISTORY OF CATTLE TICK. 27 
PARASITIC PERIOD. 
The data already given regarding the periods of preoviposition, 
incubation, and survival of seed ticks have an important bearing on 
the time required to free pastures or other inclosures from ticks pro- 
vided the cattle are removed. The data given under the present head- 
ing, on the other hand, show the time required at different seasons 
to free cattle of ticks by placing them in inclosures from which the ticks 
have been eliminated either by systematic starvation or by the use of 
naturally tick-free areas, as, for instance, fields that have been in culti- 
vation for one crop season. 
In this work we have utilized a grade Durham steer, 17 months 
old at the beginning of the experiments. (See PI. II, fig. 1.) By 
means of kerosene emulsion he was carefully cleaned of the thou- 
sands of ticks infesting him when obtained. Thereafter he was thor- 
oughly washed to remove traces of the insecticide and hundreds of 
seed ticks were applied. Under proper precautions to avoid the steer’s 
accidental infestation, these ticks were allowed to reach maturity. 
After the ticks of each infestation became adult the steer was thoroughly - 
cleaned and placed in another inclosure, which in each case had been 
carefully disinfected by means of sprays. This process has now been 
repeated until ten infestations have been reared covering the period 
between August, 1905, and March, 1907. The details are given in 
Table VII. In rotation systems the minimum developmental period 
is the most important, because the cattle must be removed before 
the earliest developed ticks have had offspring to reinfest them. 
Therefore special reference is made in the table to the shortest periods 
found, although the longest and the average are both given. 
The following deductions may be made from this table: 
1. The period from attachment to dropping ranges from 21 to 58 
days. It should be noted that in the longest periods the limit was 
reached by only one or two belated ticks, the majority approaching 
the average. 
2. The average period ranges from 26.5 to 43 days. 
3. The average parasitic period is normally some days longer in 
winter than in summer. But warm winter weather, as happened in 
infestation No. 9, may reduce the period even below the average for 
the summer. 
4. The slowest developing ticks of one infestation may occupy from 
10 days (in the summer) to 32 days (in the winter) longer than the 
most rapidly developing ones. The rapidity of development of the 
ticks of the same infestation depends somewhat upon their location. 
Those on the portions of the body where the blood supply is most 
abundant develop most quickly. In general it seems that heavy infes- 
tations develop a little more quickly than light ones. This may be 
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