﻿40 



BULLETIlSr 1374, U. S. DEPARTMENT OF AGEICULTURE 



These cylinders were kept under observation throughout the 

 summer and in October the soil was removed from them and. carefully 

 examined. Table 30 shows the results of this experiment. 



Table 30. — Emergences of moths and larvae buried at different depths in soil in 



cylinders 



Larvae buried 



Emerged during summer 



Found in soil (dead) 



Depth 



Number 



Larvae 



Pupae 



Moths 



Larvse 



Pupae 



Pupal 



cases 



Inches 



4 



8 

 12 

 16 

 20 



74 

 74 

 74 

 74 

 73 



2 





1 



17 

 15 



3 



2 



4 

 3 

 1 

 4 

 6 





4 

 1 

 3 







6 



8 

 15 



1 







1 



1 







The larvse recorded under ^'Emerged during summer" were found 

 in the traps, evidently having issued from the soil and entered the 

 screen-wire traps in searching for a place to pupate or trying to escape 

 from the cylinders. This also accounts for the one that entered and 

 later pupated. These larvse and the pupa were all dead when 

 found, having evidently been killed in the traps by the heat of the 

 sun. The adult taken from the cylinder in which the larvse were 

 buried at the depth of 4 inches was alive and perfectly devel- 

 oped. The other adult was imperfectly developed and had been 

 partly eaten by ants when found. 



Considering the number of larvse that were found to have issued 

 fromVthe soil, the most reasonable explanation of the emergence of 

 the moths is that the larvse first came to the surface, or near the sur- 

 face, and then pupated. This explanation is much more reasonable 

 than that a moth could issue from any great depth of soil unless it 

 were of such nature that the moth would not have to burrow its way 

 out. The experiment plainly shows that the pink bollworm, at least 

 in the larva stage, can escape even if buried to a considerable depth 

 by cultivation. 



SITMMEK CULTIVATION 



It was shown in Tables 25 and 26 that during the summer the 

 natural mortahty of the pink bollworm in the soil is greater for in- 

 dividuals found between the rows than for those found immediately 

 under the plants and that the mortality decreases with depth. This 

 suggested that the heat of the sun might be responsible for the in- 

 creased mortahty, since larvse between the rows, particularly near 

 the surface, are more exposed to this heat. A few experiments were 

 conducted to determine whether this is true. 



Temperature readings were taken on several days in September, 

 1921, on the surface of the soil and 1 and 2 inches below the surface 

 during the hottest part of the day. These readings are recorded in 

 Table 31. 



