﻿12 



BULLETIN 1374, U. S. DEPARTMENT OF AGRICULTITKE 



A very sudden decrease in the number of living larvae after the end 

 of January without a compensating increase in the number of dead 

 larvae is noted in both Tables 8 and 9. Few pupal cases were found 

 in any of the bolls, so this does not explain the disappearance of the 

 larvae; neither was there any increase in numbers found in the soil. 

 On January 30 the first rain, 0.34 inch, fell since the experiment was 

 started. This may have caused many larvae to leave the bolls; 

 but, owing to the condition of the soil immediately after the rain, 

 they did not enter the soil readily. Many of them were probably 

 destroyed by birds or crawled beyond the area of soil that was 

 examined. 



Tables 8 and 9 indicate that very few larvae left the bolls on the 

 stalks to go to the soil. With the larvae in the bolls placed on the 

 surface of the soil the proportion leaving the bolls was much greater. 

 As shown in Table 8, most of this entrance of larvae from the bolls 

 into the soil must have taken place shortly after the bolls were placed 

 on the soil. The first examination, six days after the bolls were 

 placed, showed as many larvae in the soil as the average for all the 

 examinations. That this may have been due to the heat of the sun 

 is indicated by the experiment about to be described. 



EFFECT OF EXPOSURE TO SUN ON ENTRANCE INTO SOIL 



On December 11, 1922, 100 bolls were placed on the surface of the 

 soil in each of two boxes filled with soil. One of these boxes was 

 kept in the shade and the other in the sun, both outdoors. Every 

 week the soil was taken from each box and carefully examined for 

 pink bollworms. Fresh soil was then put into the boxes and the 

 same bolls replaced on the surface thereof. The results of this test 

 are shown in Table 10. 



Table 10. — Number of larvse leaving 100 bolls on the surface of the soil in the shade 

 and in sun, and entering the soil 



Date examined 



Number of larvse in 

 the soU 



Date examined 



Number of larvae in 

 the soil 



In the 

 shade 



In the 

 sun 



In the 

 shade 



In the 

 sun 



Dec. 18 





 

 

 





 

 

 



2 

 6 

 3 

 

 

 

 1 

 2 

 1 

 1 



Feb. 26, 







S 





 

 

 



4 



25 



Mar. 5 



12 



19 



1 



Jan. 1. . .- -. - 







8 







15 



26 







22... 



Apr. 2 



9 







29 







Feb 5 



Total 





12 







21 



19 









The total of 21 larvae found to have entered the soil from the bolls 

 in the sun, with none from the bolls in the shade, shows clearly the 

 effect of exposure to the sun. Below (Table 11) is given a record of 

 the precipitation and the maximum daily temperature reached at the 

 surface of the soil during the time these experiments were conducted, 

 as well as the maximum daily air temperature. 



