126 



THE MEXICAN COTTON-BOLL WEEVIL. 



These zones are illustrated in the accompanying diagram (fig. 26). 



UPPER ZONE OF FATAL TEMPERATURE. 



Numerous experiments have been conducted in dropping adult 

 boll weevils upon the soil at different temperatures to determine the 



effects upon the insect. 



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In this work 119 tests 

 were made at soil tem- 

 peratures varying from 

 110° to 140° F. Below 

 122° F. none of the wee- 

 vils were killed, but from 

 122° F. upward death re- 

 sulted in times varying 

 from 1 second to 900 

 seconds. In a general 

 way the exposure neces- 

 sary to cause death de- 

 creased as the tempera- 

 tures became higher. 

 From these experiments 

 we conclude that the 

 upper zone of fatal tem- 

 perature for the adult 

 boll weevil may be con- 

 sidered as from 122° to 

 140° F. 



In the series of exper- 

 iments to which refer- 

 ence has been made a 

 number of observations 

 were made upon humid- 

 ity. The atmospheric 

 humidity during the time 

 the experiments were 

 under way, however, was 

 rather constant, ranging 

 from 37 per cent to 40 

 per cent. Within this 

 narrow range it was not 

 determined that humid- 

 ity either decreased or 

 increased the length of 

 time necessary to cause 

 the death at any fixed 

 temperature. 



It is interesting to 

 note that the zone of 

 fatal temperature for 

 adult weevils which fall 

 to the ground will be 

 reached under general conditions when the temperature recorded 

 at the usual distance above ground at which thermometers are placed 

 reaches 95° F. 



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Fig. 26.— Diagram to illustrate the zones of temperature in their 

 relations to the activities of the boll weevil. (Original. 1 



