BIOLOGY OF TOBACCO }10TH A^D ITS CONTROL 



11 



served in the laboratory was 25 days. This occurred in October, and 

 it is likely that this figure represents approximately the maximum 

 duration of the pupal period obtaining in tobacco storages. 



SEASONAL HISTORY 



In the unheated warehouses in which the writers made their obser- 

 vations the tobacco moth passed the winter as one-fourth-grown to 

 full-grown larvae. Many of those that were full-grown had 

 migrated to sheltered places about the buildings, but the undeveloped 

 larvae usually remained in the tobacco, where, dur- 

 ing periods of warm weather, they were observed 

 crawling in the tobacco leaves. It is possible that 

 they did some feeding during such periods. The low 

 winter temperatures experienced in Virginia and 

 Xorth Carolina during the period of these studies 

 (28° F. tobacco temperature and 9° warehouse tem- 

 perature) did not appear to reduce materially the 

 larval population. 



The full-grown larvae began to pupate in the to- 

 bacco warehouses in March, and the records show the 

 earliest emergences to have been as follows : In 1931, 

 May 9; in 1932, April 24; in 1933, May 2; and in 

 1934 on April 26. The emergence of the spring brood 

 proceeded at a rather slow rate until the advent of 

 hot weather, approximately May 25. 



In the laboratory this emergence covered a wide 

 span of time — for example, in 1932 from April 21 

 to July 15, and in 1933 from April 14 to July 9. 

 This long period was due in part to the fact that the 

 larvae going into hibernation in the fall were of 

 different ages, but to a greater extent to their uneven 

 rate of growth. Although the period of emergence 

 of the spring brood is extended there was a peak 

 emergence at a date around which most of the brood 

 appeared. This peak in the laboratorv occurred 

 about May 15 in 1932 and May 12 in 1933 (table 1). 

 showed that the peak of spring emergence in tobacco warehouses 

 occurred approximately 10 days later than in the laboratory — on 

 May 25 in 1932 and on May 22 in 1933. The spring brood of moths 

 mated and began egg laying soon after emergence. 



There were two complete generations of the insect in tobacco ware- 

 houses and three periods of moth emergence each year (fig. 8). A 

 small number of larvae of the first generation, approximately one- 

 half of those of the second, and all of those of the third passed 

 through the winter and emerged the following spring. There were 

 three dates in 1933 on which the peak of emergence was recorded, 

 viz. May 12 for spring-brood moths, July 22 for first-generation 

 moths, and September 18 for moths of the second generation. These 

 dates are likely to vary from year to year with environment and 

 temperature. 



Figure 7. — Pupa 

 of the tobacco 

 moth. X 9. 



Observations 



