﻿STUDIES OF THE PINK BOLLWOEM IN MEXICO 



31 



fields at the same time. The cotton at the other point also devel- 

 oped a heavy infestation. A number of families ot Mexicans lived 

 at each of these ranches, and, although supposedly no material 

 subject to infestation was ever brought there, it is extremely likely 

 that infested seed or seed cotton was brought in with packing, 

 bedding, or the like. This seems a more logical explanation, in view 

 of the early development of heavy infestation, than the theory of 

 flight. 



NATURAL CONTROL 



One of the characteristics of the pink boUworm under conditions 

 in Mexico is the regularity of its attack. Equally as characteristic 

 is the contrast between the enormous number of larvse found in the 

 fields in the fall and the slow development of the infestation in the 

 spring. Though the latter is probably explained to a great extent 

 by the practice of thoroughly cleaning the fields in the winter and 

 fumigating the planting seed, still were there not a heavy natural 

 mortahty among both the hibernating larvsB and the newly hatched 

 larvge during the season much greater damage would be expected. 



MORTALITY OF YOUNG LARV^ 



The great difference between the total eggs deposited and the 

 number of larvse found in the bolls was pointed out in connection 

 with Table 1. A greater discrepancy occurs between the number 

 of apparent entrance holes on the outside of the boll and the number 

 of worms within the boll, as shown in Table 2. These facts point 

 to a mortality of something like 90 per cent of the young larvse 

 before they enter the boll. 



The mortality of the larvse after the boll is once entered does not 

 appear, to be very high. 



Data collected during 1921 on the transformation of the pink 

 bollworm in the soil showed considerable mortality during this 

 period. In a number of soil examinations separate records were 

 kept of the findings in the soil immediately under the plants and 

 those between the rows. For further explanation of this experi- 

 ment see page 7. In other examinations the soil was divided into 

 three 2-inch layers. The results of the former are given in Table 25. 



-pABLE 25. 



-Mortality of the pink hollworm in the soil immediately under the plants 

 and between the rows 





Under the plants 



Between the rows 



Date of examination 



LarvsB and pupae 



Pupal 

 cases 



Larvse and pupae 



Pupal 





Living 



Dead 



Living 



Dead 



cases 



Auk. 19 



7 



12 ! 41 



3 

 

 2 

 2 

 3 



8 

 9 

 2 

 

 2 



44 



Sept. C 



25 : 



51 1 15 3 

 10 ! 3 5 

 1 33 



2 

 2 



Oct, 18 



8 



29 



2 



7 









Total 



70 



30 I 80 



10 



21 



01 











Total, all stages 



180 



92 













15.9 





22. 8 











