BIOLOGY OF TOBACCO MOTH AXD ITS COXTROL 



17 



The extreme incubation periods among 5,768 eggs of first-genera- 

 tion moths in 1932 were 15 and -1 days and the shortest average period 

 was 4.8 days. In 1933 with higher temperatures prevailing (fig. 10) 

 the maximum hatching period in 2,916 eggs was 12 days and the 

 minimum period 4 days. The maximum and minimum hatching 

 periods of the second generation in 3 ,186 eggs in 1932 were 13 and 4 

 days, respectively. Higher temperatures prevailed in 1933 during 

 the period covered by the second generation, and the maximum and 

 minimum incubation periods for 5,337 eggs were 9 and 3 days, respec- 

 tively. It should be pointed out, however, that second-generation 

 moths continued to emerge in 1932 until the middle of October, 

 whereas in 1933 the last emergence occurred approximately August 

 26 (table 3). The average hatching periods of eggs laid in each gen- 

 eration for the 2-year studies, excluding eggs laid by females emerg- 

 ing in October 1932, were approximately the same. Only a small 

 number of third-generation moths emerged, and many second-genera- 

 tion larvae overwintered to emerge as spring-brood moths. 



LARVAL PERIOD 



The maximum and minimum larval periods of the moths of the 

 first and second generations in 1932 and 1933 are given in table 4. 

 The higher temperatures which prevailed in May and June 1933 

 caused larvae of the first generation to complete development more 

 rapidly than the corresponding generation in 1932. 



Table 4. — Larval periods of the tobacco moth in the laboratory, Richmond, Va., 



1932 and 1933 



FIRST GENERATION 



1932 



1933 





Larvae 



Length of larval 

 period 



Aver- 

 age 



mean 

 temper- 

 ature 

 for 



larval 

 period 



Period of 



hatching « 



Larvae 



Length of larval 

 period 



Aver- 

 age 



Period of 

 hatching « 



Range 



Weighted 

 average 



Range 



Weighted 

 average 



temper- 

 ature 



for 

 larval 

 period 



May 4-11 



May 11-18 



May 18-25 



May 25- June 1. 

 June 1-8 



Number 

 20 

 41 

 125 

 51 

 15 

 3 



Days 

 59-101 

 48-128 

 39-118 

 44-117 

 46-104 

 40-49 



Days 

 77.2 

 78.4 

 75.0 

 74.3 

 69.5 

 43.3 



°F. 



76 

 70 

 69 

 73 



74 



Apr. 30-May 7 



May 7-14 



May 14-21 



May 21-28 



May28-June4. 



June4-ll 



June 11-18 



June 19 



Number 



62 



185 



250 



316 











98 



6 



Days 

 35-77 

 34-74 

 30-72 

 29-75 



Days 

 51.1 

 52.2 

 46.5 

 43.1 



°F. 

 70 

 72 

 75 

 80 

 74 



June 8-11 







83 





32-59 

 37-52 



40.9 

 42.8 



76 

 76 



SECOND GENERATION 



Aug. 14-20... 



37-49 



44.6 



80 



June 29-July 

 July6-13_— 

 July 13-20— 

 July 20-22... 



4 



25-35 



31.5 



4 



32-48 



37.0 



64 



23-66 



35.3 



4 



35-18 



41.0 



1 Records were made during the day, and the larvae that emerged in the early part of the day were counted 

 with one group and those emerging after the count were included in the following period. 



101216°— 37 3 



