﻿34 BULLETIN 1374, U. S. DEPARTMENT OF AGEICULTUEE 



Table 27. — Mortality of resting pink bollworms in the soil in the fields, 1921 and 



1922 



Month 



Percentage of 

 mortality 



1922-23 



November. 

 December - 



January 



February.. 



March 



April 



May 



June 



July 



10 



26.6 

 24.2 

 34.9 

 41.4 

 29.5 

 39.8 

 60.0 

 100 



38.9 

 22.8 

 26.4 

 26.1 

 33.1 



These records are based entirely on actual field examinations, 

 which explains their irregularity. In the first place there is an 

 accumulation of dead larvse and pupae from the summer and fall. 

 And as the larvse assume the resting stage in the soil gradually, 

 it is not possible to consider a certain percentage of the dead an 

 accumulation of the summer stages and subtract this from all sub- 

 sequent records. Again, a gradual decay of dead larvae, which are 

 consequently not found in the examinations, will make the figures 

 for dead too low in the later examinations. Lastly, emergences of 

 moths have not been considered at all in these figures, because pupal 

 cases are to a great extent destroyed in preparing the soil for exami- 

 nation. The records for 1922-23 are based on examinations of more 

 soil than those for 1921-22. Also the soil all came from the same 

 field, which was not the case in 1921-22. Individual figures for the 

 second season are therefore more comparable than for the first. 

 The decrease in the percentage of dead for December, 1922, was 

 due to the cutting of the cotton stalks at the end of November, 

 which, as has been pointed out, caused the shedding of many bolls 

 and a consequent issuance of many larvae from these bolls and 

 entrance into the soil. From data in Table 7, an increase is cal- 

 culated in the average number of living larvae and pupae per square 

 yard of soil from 6.4 for November to 18.6 for December. 



The records in Table 27 give no indication of the total mortality 

 during the resting period and the percentage of the larvae that 

 finally transform to the moth stage. In connection with an experi- 

 ment on the effect of winter cultivation, some cages were placed in 

 the field to catch moths emerging from the soil in the spring. This 

 experiment is described in detail in this report, under "Winter 

 plowing." A partly calculated record of an emergence of 2.2 moths 

 per square yard from an uncultivated part of the field which aver- 

 aged 14 living larvae per square yard during March and April is 

 given. This would show a mortality of about 84 per cent of the 

 larvae that pass the resting period in the soil. 



PARASITES 



In the spring of 1921 an experiment was started to determine 

 whether daily picking of all infested blooms would reduce the pink 

 bollworm infestation. A half-acre plat was selected for this test, 

 and work was commenced June 17. After a few days a considerable 



