Feb. '08] JOURNAL OF ECONOMIC ENTOMOLOGY 53 



tion between the daily mean temperature and the total effective re- 

 quired for hatching. An examination of careful records kept by 

 ]\Ir. Hooker extending over two entire years enables us to formulate 

 the following tentative law: When the average daily mean tempera- 

 ture ranges less than 53.2 degrees, at least 1,510.8 degrees of effective 

 temperature must accumulate before hatching will take place. When 

 the mean daily temperature averages from 61.4° to 77.8°, from 840.5 

 to 1,139.1 degrees of effective temperature will be required for hatch- 

 ing. When the mean daily temperature averages higher than 80 

 degrees, between 782.7 and 824.3 degrees of effective temperature 

 must be accumulated before hatching will take place. 



Practical Application. — In approximately one-half of the normally 

 tick infested area in this country no eggs deposited after about the 

 middle of September hatch until some indefinite time the following 

 spring. The cultivated fields (and those from which cattle have been 

 kept for some time) in this large area are absolutely free of ticks 

 every fall. Infested cattle will soon lose their ticks when placed on 

 such areas and will not become reinfested with the progeny of the 

 dropped individuals until such time as the eggs may hatch. The 

 law proposed wiU tell the farmer how long the cattle may remain 

 without danger of infestation. There has been an indefinite rule to 

 let cattle remain in such cases "until spring," but some seasons they 

 should be removed in February and in others the pasture could be 

 continued in use until May. One of the most important difficulties 

 in the rotation system of freeing cattle of ticks is that farms are 

 generally overstocked. The rule proposed will tend to minimize this 

 obstacle by showing how pastures may be utilized until the latest 

 safe date. 



The following is proposed as the most feasible plan in placing the 

 necessary information in the hands of farmers : let the state ento- 

 mologist keep records of the daily mean and effective temperatures 

 (or obtain them from the Weather Bureau) beginning with, say Sep- 

 tember 15 and starting separate computations at regular semi-monthly 

 intervals. These dates will stand for the time when any farmer may 

 have placed cattle in tick free areas. When the proposed law shows 

 that the time for eggs to hatch is approaching, notice could be issued 

 in the press. Such a notice might read in brief as follows : Farmers 

 who placed cattle in tick free areas between September 15 and 30 

 should remove them by February 15 ; there is no danger of reinfesta- 

 tion of cattle placed on tick free pastures during October and will 

 not be until further notice is given. 



It is not at all improbable that individual ranchers could apply 

 the rule by means of data obtained on their own places. In such 



