130 



THE MEXICAN COTTON-BOLL WEEVIL. 



Fig. 29.— Map showing minimum temperatures on Octo- 

 ber 29 and 30, 1910, the date of the first killing frost in 

 Louisiana. (Original.) 



the normal dates of the first killing frosts. Comparison of these two 

 maps will show at a glance that the first killing freeze of 1910 was over 

 a month earlier than the normal. Such a natural phenomenon is an 

 exact equivalent of artificial fall destruction at the same date. The 



temperatures were not fatal 

 to the weevils, but were 

 such as to force hibernation 

 and at the same time cut 

 off food supply. If tem- 

 peratures compelling hiber- 

 nation had continued, the 

 weevils would have emerge p 

 in about the same propor- 

 tion as would be expected 

 if they were artificially de- 

 prived of food on the same 

 date. However, another 

 climatic factor intervened. 

 Almost the entire month 

 of November was warm, and 

 throughout Louisiana, at 

 least, the mean temperature 

 stood at above 56° F. for the 

 month. We have already 

 shown that a continuance 

 of mean temperatures over 

 56° F. will force the weevils to take food, and that in the absence of food 

 at effective temperatures starvation occurs in a few days. If all of 

 the cotton had been killed by the freeze, the control would have been 

 complete, but there are al- 

 ways sheltered areas on 

 hillsides or near buildings 

 that escape two or three 

 severe freezes, and these 

 areas no doubt harbored 

 many weevils until the 

 cold wave of November 29 

 drove them to a normal 

 hibernation. 



In the map (fig. 29) show- 

 ing the Louisiana minimum 

 temperatures of October 29 

 and- 30, 1910, on which 

 dates the first killing frost 

 occurred, it will be noticed 

 that no fatal temperature 

 was reached, but that a 

 freezing temperature oc- 

 curred in practically all of 

 the cotton-producing terri- 

 tory. The other map (fig. 30) illustrates the minimum temperatures 

 of the 1 entire winter of 1910-11 and shows that fatal temperatures 

 (7° F. to 22° F.) occurred throughout the State. These minima 



Fig. 30. 



Map shov.ing minimum temperatures in (he winter 

 of 1910-11 in Louisiana. (Original.) 



