METHODS OF CONTROLLING TOBACCO INSECTS. 



Table I. — Average length of different stages in life history of the southern tobacco 

 hornvorin (Pilegethontius sexto). 





Fig. 9. 



The Southern tobacco hornworm: Larva, fourth instar. Natural 

 size. (Original.) 



The tobacco moths, as has already been stated, begin to emerge 

 from hibernation about June 1, or slightly earlier, and the emgrgenct 

 continues until the middle of August or later. From Table I we see 

 that 48 days after the emergence of the moths from hibernation the 

 moths of the second generation will become adult, and that in 4 days 

 more they will begin to deposit eggs. These egos will hatch in 4 

 days, and in 6 or 7 days more — that is, in about two months from the 

 emergence of the first moths from hibernation —the larva 1 of the 

 second generation will pass into the third instar, the instar in which 

 they begin to injure tobacco seriously. For example, let us take 4 

 moths that have 

 emerged from hi- 

 bernation on the 

 following dates: 

 June 1, June 15, 

 July 1, and July 

 15. The second 

 generation of to- 

 bacco worms, the progeny of these moths, will begin to injure 

 tobacco seriously about August 1, August 15, September 1, and 

 September 15, respectively. 



Although moths of both the first and second generations are 

 depositing eggs during late July and in August, we will show later 

 that by far the greater percentage of them has just emerged from 

 hibernation, and belongs, therefore, to the first generation. This 

 fact has a very important bearing upon the recommendation of fall 

 plowing. 



Tobacco worms begin to enter the soil to pass the winter (i. e., 

 hibernate) about the middle of August, and continue doing so until 

 frost. Usually they penetrate the soil to a depth of from 3 to 6 

 inches. Several observations upon "second bottom" soils of the 

 Cumberland River have shown the average depth to be 4 inches; th.it 

 is, to nearly the greatest depth to which the land was plowed in pre- 



Note. — For the purposes of this article the date of pviposition may be considered as 

 taking place at any time from June 1 to July 15, for there will not be a second genera- 

 tion from eggs deposited after the latter date. 



