16 



CIRCULAR 4 2 2, U. S. DEPARTMENT OF AGRICULTURE 



(Table 1.) The higher temperature during April, May, and June in 

 1933 apparently accelerated the development periods and were re- 

 sponsible for the fact that a much larger number of individuals com- 

 pleted the third generation in that year. The higher temperatures 

 prevailing in September and part of October also contributed to the 

 growth of moths of the third generation. As shown by incubation 

 records in table 3. first-generation eggs were laid 5 days earlier in 

 1933 whereas the second and third generations appeared 25 days and 

 49 days, respectively, earlier in 1933 than in 193*2. 



INCUBATION PERIOD 



Incubation periods of eggs of the first, second, and third genera- 

 tions of moths were recorded in 1932 and 1933 and a summary of 

 these records is shown in table 3. 



Table 3. — Incubation periods of eggs of the tobacco moth in the laboratory, 

 Richmond, Va., 1932 and 1933 



FIRST GENERATION 



1932 



1933 





Eggs 



Incubation 

 period 



Aver- 

 age 

 mean 

 tem- 

 pera- 

 ture 

 for 

 period 



Period eggs 

 were laid 1 



Eggs 



Incubation 

 period 



Aver- 

 ' age 



mean 



Period eggs 

 were laid l 



Range 



Weight- 

 ed aver- 

 age 



Range 



Weight- 

 ed aver- 

 age 



tem- 

 pera- 

 ture 

 for 

 period 



Apr. 23-30 



Apr. 30-May 7.. 



May7-14 



May 14-21 



May 21-28 



May 28-June4_. 



Num- 

 ber 

 39 

 319 

 1,918 

 1,648 

 ' 1,008 

 233 

 118 

 240 

 211 

 34 



Days 

 10-12 

 7-11 

 8-14 

 7-15 

 6-12 

 5-10 

 5- 8 

 5- 7 

 5- 6 

 4- 6 



Days 

 11.0 

 7.9 

 9.1 

 8.6 

 7.2 

 7.1 

 6.9 

 5.9 

 5.3 

 4.8 



°F. 

 56 

 73 

 72 

 71 

 74 

 72 

 77 

 77 

 78 

 82 



Apr. 18-25 



Apr. 25-May 2. - 



May 2-9 



May 9-16 



May 16-23 



May 23-30 



May 30- June 6„ 



June6-13 



June 13-15 



Num- 

 ber 

 31 

 270 

 764 

 659 

 657 

 

 

 503 

 32 



Days 

 9-12 

 8-10 

 8-10 

 5-10 

 6- 9 



Days 

 11.0 

 8.6 



8.8 

 6.3 

 6.9 



°F. 

 60 

 67 

 69 

 75 

 74 

 80 



June 4-11 _ . 







74 



June 11-18 



June 18-25 



June 25-28 



4-10 



7- 9 



5.4 

 8.1 



84 

 75 



SECOND GENERATION 



Jul v 20-27 



July 27-Aug. 3, 



Aug. 3-10 



Aug. 10-17 



Aug. 17-24 



Aug. 24-31 



Aug. 31-Sept. 7_ 



Sept. 7-14 



Sept, 14-21 



Sept. 21-28 



Sept, 28-0ct. 5__ 



Oct. 5-12 



Oct, 12-18 



618 



4- 8 



5.2 



83 



453 



4- 7 



4.9 



82 



397 



4- 7 



4. 1 



84 



334 



4- 7 



' 5.0 



81 



484 



5- 8 



6.3 



78 



394 



4- 6 



4.4 



83 



158 



4- 7 



5.5 



86 



103 



5- 7 



6.6 



73 



125 



5- 7 



6.1 



75 





 16 







74 

 69 



12-13 



12.5 



77 



10-12 



11.5 



68 



27 



8-10 



8.3 



62 



June 25-July 2 



July 2-9 



July 9-16 



July 16-23 



July 23-30 



July 30-Aug. 6 



Aug. 6-13 



Aug. 13-20 



Aug. 20-26 



91 



3-4 



3.5 



896 



4-6 



4.8 



2.838 



5-9 



5.7 



981 



3-7 



4.5 



62 



4-5 



4.3 





 164 







4-6 



5.0 



222 



4-7 



5.2 



83 



4-7 



4.4 



THIRD GENERATION 



Oct. 9-18. 



90 



8-14 



63 



Aug. 21-28 



Aug. 28-Sept, 4 



Sept. 4-11 



Sept. 11-18 



373 



4-7 



4.8 



80 



129 



5-6 



5.5 



78 



155 



4-6 



4.6 



82 



209 



4-7 



5.9 



79 



1 Records were made during the day, and those eggs that were laid in the early part 

 of the day were counted with one group and those laid after the count were included in 

 the following period. 



