ECONOMIC ZOOLOGY — ENTOMOLOGY. 459 



ture conditions, whicli have proved fatal in tlie Northern States, prevail over 

 any portion of the territory now infested a large i)ercentage of those not upon 

 the host will be destroyed. When upon the host, however, the stages are not 

 seriously affected by low temperatures, for the body heat of the host animal 

 tends to offset the cold of the surrounding air. Twenty-four degrees F. was 

 the highest temperature at which adult ticks were killed. At 17° all of 139 

 adult ticks exposed were killed, and at 16° and 15°, 91 and 92 per cent, respec- 

 tively. All of the adult ticks exposed at 14° were killed as well as those at 13°, 

 12°, and 8°, thus the author assumes that 14° is fatal to all exposed adult ticks. 

 It was found that ticks that have laid a part of their eggs are most easily 

 killed by cold than those that have not commenced oviposition. 



"Adult ticks proteced by a covering of chaff or fine litter, such as would 

 be found about stables or barnyards, are able to endure much lower tempera- 

 tures [12°] than those exposed to the air. If the cover be damp, however, they 

 will be killed almost as readily as if unprotected. In barnyards the litter is 

 very liable to be moist, if not wet, and as a consequence there is little danger 

 of adult ticks in such situations surviving the winter. This is also true for 

 ticks that drop from host animals on pastures and woodlands, for the leaves 

 and other soil coverings are very liable to be excessively wet during the winter. 

 In the stables, on the other hand, the litter or chaff is more than likely to be 

 dry. , . . 



" Ticks dropping from the host during the period when the daily mean tem- 

 perature is between 75° and 69° lay eggs which may hatch the same season or 

 may go over until the following spring, depending upon the temperatui'e during 

 the fall and winter months. Ticks dropping from the host after the tempera- 

 ture has fallen below 69° may lay eggs if not killed by freezing, but these 

 eggs will remain dormant during the winter, hatching in the spring. In our 

 investigations here we have found that engorged ticks dropping from the host 

 animal during a short period in late fall have their egg laying interrupted 

 several times by low temperatures and are finally killed by freezing before 

 the process is completed. Those eggs which they do lay fail to hatch. Fol- 

 lowing this period is another during which all of the ticks are killed by freez- 

 ing before egg laying has begun. This period is longest on the extreme north- 

 ern edge of the tick area, becoming gradually shorter as one proceeds south- 

 ward, until it disappears entirely under average conditions along the Gulf 

 Coast." 



The author has found that the water content makes up about 75 per cent of 

 the weight of the normal egg. Experiments showed that when more than 25 

 per cent of the original weight of the eggs was lost they would not hatch. It 

 was found that when unprotected by chaff, litter, or other mulches 78 per cent 

 of the eggs were destroyed at 4° above zero and all are destroyed at 2° above. 

 Forty-six per cent of the larvae were killed at 8° above zero and all at 4° above. 



Relation of climate to life history, J. F. Voorhees (pp. 132-164). — The 

 author has made a study of the relation of temperature to the development and 

 control of the cattle tick, using the data published by H. A. Morgan (E. S. R., 

 10, p. 389; 11, p. 588) ; Hunter and Hooker (E. S. R., 19, p. 664) ; Newell and 

 Dougherty (E. S. R., 18, p. 987) ; and the author of the first part of this bulle- 

 tin, on the life history of the tick ; and the temperature records of the Weather 

 Bureau of this Department, as a basis. 



The methods followed are briefly described and illustrated. Charts have 

 been platted which show the time necessary for the cleaning up of pastures 

 by the starvation of seed ticks, beginning with the first of each month, and th£ 

 average date when eggs laid the first of any month may be expected to hatch at 

 various localities in the tick-infested area. Maps are also given which show 



