30 



BULLETIN 231, U. S. DEPARTMENT OF AGRICULTURE. 



Table XIX. — Number of generations of the boll weevil — maximum series on squares. 

 [First generation from first eggs of females that emerged from hibernation May 8 to 10.] 



Generation. 



Date. 



Mean tem- 

 perature for 

 period. 1 



Period from 



maturity to 



maturity 



(about). 



First generation: 



May 

 June 



June 

 July 



July 

 July 



July 

 Aug. 



Aug. 

 Sept. 



Sept. 

 Sept. 



Oct. 

 Nov, 



19-24 



4- 8 



17-22 



1- 4 



7-10 

 20-22 



27-30 

 9-11 



19-22 

 3-5 



8-10 

 27-29 



7-11 



2- 4 



o F 



Days. 





78.2 



28 



Second generation: 



Eggs laid 







80.1 



26 



Third generation: 







84.3 



19 



Fourth generation: 



Eggs laid 







87.5 



20 



Fifth generation: 



Eggs laid 







85.2 



25 



Sixth generation: 



Eggs laid 





Generation mature 



76.5 



24 



Seventh generation: 







69.8 



36 







1 The period referred to here is that from the "average time of emergence of a generation to the same 

 time in the next generation. 



The weevils were very unusually late in emerging from hiberna- 

 tion at Victoria in the spring of 1913, the first being found on May 8. 

 This is at least two or three weeks later than the usual time. As a 

 result, nearly one complete generation was cut off the first of the 

 season. The last generation secured in the breeding series was the 

 seventh. The adults of this generation emerged November 2 to 4. 

 At this time the cool weather had practically stopped all breeding 

 in both cages and field, and this was considered to be the last gener- 

 ation. However, the weather became warmer in the latter part of 

 November and December, and on the 26th of December Mr. J. D. 

 Mitchell found breeding in progress in the field. This was evidently 

 a case of an extra generation caused by the unusually warm weather 

 after the starting of hibernation. The maximum number of genera- 

 tions in squares at Victoria in a normal season is evidently seven or 

 eight. 



The minimum generation series was conducted quite differently. 

 The last eggs were secured from the hibernated females used in start- 

 ing the maximum series. The last adults reared from these eggs were 

 mated and their last eggs secured. The results of this series are 

 shown in Table XX. The last adults of the second generation did 

 not mature until October 13 to 15, and as these certainly would enter 

 hibernation this was considered as the minimum number of genera- 

 tions from the first hibernated females. As the last females to 

 emerge from hibernation in the spring would continue ovipositing 

 much longer and the last weevils of the first reared generation would 

 mature much later in the season, it seems quite possible for weevils 

 of the first generation to enter hibernation in the fall. 



