STUDIES OF THE PINK BOLLWORM IN MEXICO 
31 
fields at the same time. The cotton at the other point also devel- 
oped a heavy infestation. A number of families of 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 bollworm under conditions 
in Mexico is the regularity of its attack. Equally as characteristic 
is the contrast between the enormous number of larvae 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 
mortality among both the hibernating larvae and the newly hatched 
larvae during the season much greater damage would be expected. 
MORTALITY OF YOUNG LARV/E 
The great difference between the total eggs deposited and the 
number of larvae 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 larvae 
before they enter the boll. 
The mortality of the larvae 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. 
Table 25. — Mortality of the pink bollworm in the soil immediately under the plants 
and between the rows 
Under the plants 
Between the rows 
Date of examination 
Larvae and pupae 
I Pupal 
Larvae and pupae 
Pupal 
Living 
| cases 
Dead | 
Living 
Dead 
cases 
Aug. 19 
7 
51 
10 

2 
12 41 
15 | 3 
3 1 5 
33 
7 
3 

2 
2 
3 
8 
9 
2 

2 
44 
Sept. 6 .. 
2 
25 .. 
2 
Oct. 18 
8 
29 , ... 
5 
Total._ . . .. 
70 
30 i 89 
10 
21 
61 
Total, all stages . 
Percentage dead. 
189 
15.9 
