96 THE MEXICAN COTTON-BOLL WEEVIL. 



time must be considered. As a matter of fact, the total number of 

 weevils in a locality on October 1 would be the number present in the 

 cotton fields on September 15, less the total number dying between 

 September 15 and October 1, and less the number leaving the field to 

 enter into hibernation during that period, plus those that matured 

 during the same time. It is likely that the number of weevils matur- 

 ing is generally sufficient to offset the number that die from natural 

 causes. This leaves only the weevils which escape collection by 

 entering into hibernation to be considered. As there is no way in 

 which this number can be determined, the method we have followed, 

 which ignores them altogether, is the closest approximation we can 

 make to a determination of the actual number of weevils which suc- 

 ceed in passing the winter after the destruction of the food plants in 

 the fall. 



It is to be noted that the possible error in the interpretation of the 

 results of hibernation experiments becomes greater in the case of 

 the cages installed late in the season. As the season advances more 

 and more of the weevils leave the fields and thus pass out of considera- 

 tion in connection with the number collected and placed in the cages. 



The hibernation experiments conducted have dealt with 181,932 

 weevils utilized in seven different seasons in seven localities through- 

 out the infested territory. 



ENTRANCE INTO HIBERNATION. 

 SOURCES OF WEEVILS ENTERING HIBERNATION. 1 



Following the maturity of a considerable portion of the crop of 

 bolls, and usually in connection with the occurrence of a heavy rain- 

 fall, a renewed growth of the plant commonly produces an abundance 

 of squares. It is this late top growth of the plant, which serves no 

 good purpose so far as further production of cotton is concerned, that 

 is primarily responsible in most fields for the needlessly large number 

 of weevils produced between the time of maturity of the crop and the 

 usual time of destruction of the plants by frost. A large proportion 

 of the weevils which become adults before September 1 may be ex- 

 pected to die, either as cold weather comes on or during the early 

 Eart of the winter season. There is no particular hibernation brood, 

 ut representatives of all generations may survive and enter hiberna- 

 tion, as has been shown by figure 14 in the discussion of the life cycle. 



STAGES ENTERING HIBERNATION. 2 



The reproductive activity of the weevil continues steadily until 

 the plants are destroyed by frost, but it gradually decreases coinci- 

 dently with the gradual decrease in temperature. All stages from 

 the egg to the adult may be found in both squares and bolls, even 

 after frosts have occurred. The immature stages in squares are not 

 immediately killed unless the freeze is exceptionally severe, and in 

 some localities many of these survive to reach maturity and to 

 emerge during the following spring. Usually, however, only those 

 which are nearly adult at the time frost occurs may be expected to 



1 The matter in this section is mainly extracted from Bull. 77, Bureau of Entomology, pp. 12, 13. 

 8 The matter in this section is largely extracted from Bull. 77, pp. ):',, 14. 



