76 THE MEXICAN COTTON-BOLL WEEVIL. 



hibernation time arrives. Most of the weevils of the first two or three 

 generations have probably died, or then do so, while most of the 

 adults of later generations, still having considerable vitality, go into 

 hibernation. It is certain that every generation may have some 

 direct part in the production of weevils which are to hibernate. All 

 weevils which are still strong and healthy when cold weather comes 

 on may be expected to go into hibernation, so that there can be no 

 special brood for this purpose. 



POSSIBLE ANNUAL PROGENY OF ONE PAIR OF HIBERNATED WEEVILS. 



One of the most important factors in the development of an insect is 

 its capacity for very rapid production. The conclusions as to the 

 ability of the boll weevil in this respect are drawn from the following 

 data, summarized from what has been set forth in preceding pages 

 of this bulletin. The starting point is considered to be the average 

 date of deposition of one-half of the eggs for the first generation at 

 Victoria, Tex., which, under the usual conditions, seems to be about 

 June 10. The average number of eggs deposited by a female was 

 found to be 139. For the purpose of this computation 70 is the 

 assumed number. The difference may be considered as an allowance 

 for mortality or failure to hatch. The average period of development 

 for each generation is 19 days. The average period between emer- 

 gence of the adult and deposition of the first eggs is 6 days. The 

 average period for the deposition of one-half the eggs for each genera- 

 tion is 18 days, thus making the average period for each generation 43 

 days. The sexes are produced in approximately equal numbers. 

 For the sake of conservatism allowance has been made for only four 

 generations in a season. The following table shows the rate of multi- 

 plication and the corresponding dates: 



Annual progeny of one pair of hibernated weevils. 



Weevils. 



First generation, average adult June 29, numbering 70 



Second generation, average adult Aug. 10, numbering 2, 450 



Third generation, average adult Sept. 22, numbering 85, 750 



Fourth generation, average adult Nov. 4, numbering 3, 001, 250 



Total 3, 089, 520 



As a matter of fact, the multiplication during the early part of the 

 season is so much more rapid that it is very certain that a large part 

 of the third generation becomes adult by the middle of August. Pos- 

 sibly a more definite idea of the significance of this ability for repro- 

 duction may be obtained if we consider that, at the conservative rate 

 given, the progeny from one fertile hibernated female might, in the 

 course of four generations, number one weevil for every square foot 

 of area in a 75-acre field. 



As a matter of fact, the possibility of the multiplication is controlled 

 primarily by the abundance of food supply. The maximum infesta- 

 tion is usually reached some time in August. If we assume that there 

 are 6,000 plants on each acre of ground, and that each plant produces 

 100 squares for weevil attack up to August 1, we would find that if 

 the usual percentage of these squares produces weevils, the actual 



