STUDIES OF THE PINK BOLLWORM 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 OF RESTING LARVAE IN THE FIELD 
An experiment is now under way which will give data on the 
mortality of resting larvae 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 
Fig. 11. — Comparative mortality of resting larvae in bolls on the surface of the soil and of resting 
larvae in the soil. Each bar represents the results of the examination of a separate lot of 100 
bolls, that had been placed on the soil on November 28, and the soil underneath. The first 
examination shows the content of 100 bolls 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 
in 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 this 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 larvae in seed and bolls on 
and in the soil of irrigated and unirrigated fields. The results of 
this experiment are discussed under " Irrigation ;; as a control method. 
In Table 27 are given the percentages of the stages in the soil 
found to be dead during the winter and spring months in 1921 and 
1922. 
