97 



POSSIBLE ANNUAL PP.OGENY 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, sum- 

 marized 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, 100 is the" assumed number. The differ- 

 ence 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 emergence of the adult and deposi- 

 tion of the first eggs is 6 days. The average period for the. deposition 

 of one-half the eggs for each generation 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 multiplication and the corresponding 

 dates: 



Annual progeny of one pair of hibernated weevils. 



Weevils. 



First generation, average adult June 29, numbering 100 



Second generation, average adult August 10, numbering 5, 000 



Third generation, average adult September 22, numbering 250, 000 



Fourth generation, average adult November 4, numbering 12, 500, 000 



Total 12, 755, 100 



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 progen}^ from one fertile hibernated female might, in the 

 course of four generations, number three weevils for every square foot 

 of area in a 100-acre field. 



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

 primarily by the abundance of food supply. As may be seen by ref- 

 erence to Table XXIX, page 114, the maximum infestation 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 per- 

 centage of these squares produce weevils, the actual multiplication 



16780— No. 51—05 7 



