128 



THE MEXICAN COTTON-BOLL WEEVIL. 



days at 44° to 45° F. made 36 feeding punctures, or at the rate of one 

 puncture every 8.4 days. It is probable that these punctures were all 

 made possible by the removals from refrigeration for examination. 



LOWER ZONE OF FATAL TEMPERATURES. 



In 1904 Dr. W. E. Hinds conducted experiments in the effects of 

 low temperature on eggs and young larvae. He found that 34 eggs at 

 45° F. for 13 to 14 days did not hatch when kept later at a temper- 

 ature of 69° to 70° F. Recently hatched larvae, however, were killed 

 by nine days' exposure to 45° F. 



By experiments conducted with adults in 1905 it was ascertained 

 that 32° F. was not fatal; 24° F. benumbed the weevils, but they could 

 revive; 18° F. killed. 



In experiments conducted by Mr. H. P. Wood 32 weevils were 

 exposed to a minimum of 15° F. and an average temperature of 18.6° 

 F. for seven and one-fourth hours and then placed in the refrigerator 

 at a higher temperature, but none recovered. 



In similar experiments Mr. W. A. Hooker exposed 11 weevils for 

 six hours to temperatures varying from 15° to 20° F. The weevils 

 were quiet, but later showed signs of life, although they died within 

 two days. Between 7 and 10 degrees, five weevils were killed in six 

 hours. One degree below zero was absolutely fatal. 



Observations on the effects of low temperatures upon the weevils in 

 the fields leads to the statement that all places experiencing a tem- 

 perature under 12° F. in the early part of the winter will profit by an 

 almost complete extinction of the weevil, depending somewhat, of 

 course, upon the amount of protection the weevils may have secured 

 before the freeze. Regions having a normal minimum temperature 

 of zero need have little fear of serious continued depredations from 

 the weevil until the insect has proved itself able to adapt itself to 

 colder temperatures than it is now able to withstand. 



In this connection it will be of interest to submit Table LXI, giving 

 the average winter mortality from cold since the beginning of our 

 records. 



Table LXI. 



• Weighted average cold control of immature stages of the boll weevil, by 

 months. 



It should be noticed that winter cold is, on the average, almost twice 

 as effective as summer heat. 



The history of the boll weevil furnishes several examples of winter 

 control, principal among which are the early freezes of November, 

 1907, November, 1908, and December, 1909* which greatly reduced 

 weevil damage in large sections. 



