﻿STUDIES OF THE PINK BOLLWOEM IN MEXICO 



33 



percentage of- living larvae in the bolls of the 1921 crop than in those 

 of 1920 may be explained in a similar way. The former were stored 

 about four months earlier in the season than the latter and were 

 therefore longer subjected to the attack of mites. 



MORTALITY OP RESTING LARVAE IN THE FIELD 



An experiment is now under way which will give data on the 

 mortality of resting larvas in the field in bolls, both on the stalks 

 and on the soil, as well as in the soil. Data on this experiment are 

 given in Tables 8 and 9. Figure 11 shows graphically the results 

 of the experiments with the bolls on the surface of the soil as recorded 



c\( ^ ^ 55 |!(J QO 



I U H I I M I I 



Fig. 11. — Comparative mortality of resting larvse in bolls on the surface of the soil and of resting 

 larvse in the soil. Each bar represents the results of the examination of a separate lot of 100 

 bolls, that had been jjlaced on the soil on November 28, and the soil underneath. The first 

 examination shows the content of 100 boUs at the time they were placed on the soil but before 

 any larvae had left them to enter the soil 



in Table 8, up to April 2. The rate of mortality is seen to be higher 

 m the bolls than in the soil. This diagram does not take into con- 

 sideration individuals that have emerged. This, however, appears 

 not to have been great to the date of the last record, as will be ob- 

 served in the record of pupal cases in Table 8. It would appear 

 from tliis that larvae left undisturbed in the soil during the resting 

 period have a better chance of surviving than those in the bolls on 

 the surface of the soil at the same time. 



Another experiment, conducted in the winter of 1921-22, dealt 

 primarily with the longevity of resting larvic in seed and bolls on 

 and in the soil of irrigated and unirrigatcd fields. The results of 

 this experiment are discussed under "Irrigation" as a control method. 



In Table 27 are given the percentages of the statues in the soil 

 found to he dead during the winter and spring montlis in 1921 and 

 1922. 



