96 HIBERNATION OF THE COTTON BOLL WEEVIL. 



and has been found to vary in different seasons and localities, occa- 

 sionally being as high as 50,000 weevils per acre, or an average of from 

 7 to 10 weevils per plant. An average of the results in 17 of the 

 most carefully studied fields shows 8,552 weevils per acre, or slightly 

 more than 1 weevil per plant. 



The proportion between the numbers of weevils hibernating on the 

 stalks and among rubbish scattered on the surface of the ground 

 changes as the season advances, the number on the stalks decreasing. 



Great mortality occurs soon after the weevils enter hibernation, 

 especially among those upon the surface of the ground. 



Hibernation usually takes place as the mean average temperature 

 falls below 55 degrees and may remain complete until the mean 

 temperature rises above 60 degrees. 



Weevils may avail themselves of almost any kind of shelter, and 

 the favorable character of the shelter in relation to prevailing cli- 

 matic conditions will influence the percentage of survival. Many 

 pass the winter sheltered by the old bolls that remain hanging upon 

 the stalks. The percentage of survival in bolls decreases generally 

 from southern to northern Texas. Bolls are frequently so important 

 a factor in shielding weevils from one season to another that it is 

 advisable to destroy them as a regular practice even in northern 

 Texas. 



Exceptionally cold and wet winter weather is most unfavorable for 

 weevil survival. The destruction of possible shelter through clean 

 culture in the fall is an effective way of reducing weevil injury to the 

 following crop. The shelter to be found in timber fringes around 

 cotton fields is much more difficult to remove or control than is that 

 within the fields. The importance of such unavoidable conditions 

 may be minimized by judicious cleaning up and by rotation of crops. 



Occasionally weevils may survive in stored cotton seed and be dis- 

 tributed along with it at planting time. This fact justifies the main- 

 tenance of quarantine regulations against the free movement from 

 infested to uninfested territory of cotton seed and closely related 

 cotton products which are apt to shelter weevils. 



Most of the information obtained in regard to the hibernation of 

 the weevil has resulted from cage experiments in which the influential 

 conditions could be separated and to some degree brought under 

 control. 



During the winter of 1902-3, at Victoria, Tex., in the small-cage 

 experiments with 356 weevils, an average of about 11 per cent sur- 

 vived. During the following season, also at Victoria, among 400 

 weevils but one-fourth of 1 per cent survived. During the winter of 

 1904-5 larger numbers of weevils were under observation at each of 

 six locahties ranging from the southern to the northern portions of 



