28 



BULLETIN 427, U. S. DEPARTMENT OF AGRICULTUEE. 



A fairly average record of a pair of adults which mated October 

 29, 1914, is as follows: 



October 31. — 40 eggs. 



November 1. — 63 eggs. 



November 2. — 28 eggs. 



November 4. — 41 eggs. 



November 5. — 18 eggs. 



November 8. — 19 eggs. Male dead. 



November 10. — 6 eggs. 



November 12. — 3 eggs. 



November 13.- — eggs. Female dead. 



SEASONAL HISTORY. 



NUMBER OF GENERATIONS. 



The number of generations in one year, as might be expected, is 

 subject to the wide irregularity shown in the separate stages, and to 

 temperature and other natural influences. 



By taking the first to emerge from each brood, six generations are 

 theoretically possible. In reality this would include five complete 

 generations, and the beginning of the sixth. 



By starting several generations in each month for almost three 

 years, it was possible to determine the average length of generations 

 for the different months of the year. 



Table 7 gives the results obtained: 



Table 7. — Length of generations of the potato tuber moth. 



Month of starting 

 generation. 



January . 

 February 

 March . . . 

 April 



Approxi- 

 mate 

 length of 

 genera- 

 tion. 



Days. 



90 



Month of starting 

 generation. 



June . - . 

 July.... 

 August, 



Approxi- 

 mate 

 length of 

 genera- 

 tion. 



Days. 



50 



40 



30-35 



30-35 



Month of starting 

 generation. 



September 

 October. . . 

 November 

 December. 



Approxi- 

 mate 

 length of 

 genera- 

 tion. 



Days. 



45 



70-75 



92 



95 



Consecutive generations for a year, using the first to emerge, may 

 be plotted as follows: 



1st Gen. 



2nd Gen. 



Plot A. 

 3d Gen. 4th Gen. 5th Gen. 



6th Gen. 



Feb. Mar. 



Apr. 



May. 



June. July. Aug. Sept. Oct. Nov. Dec. 



This shows plainly that even in the more severe years six genera- 

 tions may be obtained, usiug the first to emerge from each brood. 



By using the last to emerge from each brood, the number of genera- 

 tions is reduced as the following plot shows. 



