BIOLOGY OF TOBACCO MOTH AND ITS CONTROL 



13 



that had been forced through a 48-mesh screen were added as food. 

 In the studies of 1931 it was found that young larvae often experi- 

 enced difficulty in feeding on tobacco leaves low in moisture content. 

 This was overcome by using screened tobacco, since this retained 

 moisture for a longer time than pieces of unscreened tobacco leaves. 



SPRING EMERGENCE, 1932 



During November 1931, 452 larvae were placed in hibernation cages 

 in the laboratory, and records of spring-brood emergence were ob- 

 tained from these in 1932. Of this number, 430 survived and pupated, 

 and 388 moths emerged. A total of 406 larvae survived the following 

 winter and emerged in the spring of 1933. Records of emergence of 

 spring-brood moths in the laboratory for 1932 and 1933 are o-iven in 

 table 1. 



Table 1. — Records of emergence of the spring brood of the tobacco moth in 

 1932 and 1933 in the laboratory, Richmond, Ya. 



Period of emergence 



Cumulative 

 emergence 



Sex 



Male 



Female 



j-to-adult period 

 of moths 



Maxi- 

 mum 



Mini- 

 mum 



Mean 

 average 

 tempera- 

 ture of 

 emer- 

 gence 

 period 



1932 



Apr. 21-28 



Apr. 28-May 5. .. 



May5-12 



May 12-19 



May 19-26 



May 26- June 2. ... 



June 2-9 



June 9-16 



June 16-23 



June 23-30 



June30-July 7 



July 7-14 



July 15 



Total 



1933 



Apr. 14-21 



Apr. 21-28 



Apr. 28-May 5..-. 



May 5-12 



May 12-19 



May 19-26 



May 26-June2..-. 



June 2-9 



June 9-16 



June 16-23 



June 23-30 



June30-July 7 



July 7-9 



Total 



Number 

 4 

 23 

 160 

 287 

 342 

 360 

 373 

 380 

 383 

 383 

 386 

 387 



388 



4 

 23 



115 

 217 

 312 

 357 

 364 

 381 



403 

 403 

 406 



Percent 



1.0 



5.9 



41.2 



74.0 



88.1 



92.8 



96.1 



97.9 



98.7 



98.7 



99.5 



99.7 



100.0 



Number 

 1 

 14 

 71 

 76 

 23 



Number 

 3 

 5 



Days 

 287 

 294 

 321 

 324 

 331 

 338 

 326 

 333 

 317 



Days 

 264 

 268 

 260 

 269 

 273 

 286 



295 



353 

 358 



310 

 358 



207 



LSI 



1.0 



5.7 

 28.3 

 53.4 

 76.8 

 87.9 

 89.7 

 93.8 

 96.1 

 97.5 

 99.3 

 99.3 

 100.0 



352 

 360 

 364 

 380 

 373 

 380 

 282 

 295 

 298 

 305 

 305 



234 

 241 

 246 

 251 

 243 

 265 

 241 

 239 

 236 

 258 

 252 



279 



273 



206 



1 Records were made during the day, and those moths 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. 



As shown in table 1, the first emergence of spring-brood moths 

 occurred on April 21 in 1932 and on April 14, or 1 week earlier, in 

 1933. On June 9, 1932, 96.1 percent had emerged, while on the same 

 date in 1933, 93.8 percent of the brood had emerged. The generally 

 warmer weather that prevailed in 1933 did not appear to affect greatly 

 the rate of spring emergence, but it is likely that this factor was 

 responsible for the emergence beginning 1 week earlier. Some of the 



