STUDIES OF THE PINK BOLLWORM IN MEXICO 
23 
point of note is the effect an infestation by the boll weevil has on the 
percentage of nonpickable cotton. This insect severely damaged 
several fields in 1921. When the attack occurs reasonably early and 
the weevil becomes abundant, it destroys the greater part of the late 
crop, allowing very few late bolls to remain on the plant. Then we 
have a condition represented by a short early crop only slightly 
damaged by the pink bollworm and very little nonpickable cotton on 
account of the lack of late bolls. This occurred in the case of planta- 
tion No. 19 in 1921, where the percentage nonpickable in the unirri- 
gated field is twice as great as in the irrigated. 
RELATION OF THE AMOUNT OF NONPICKABLE COTTON TO TOTAL DAMAGE 
A seasonal variation in the ratio of nonpickable cotton to total 
damage may be looked for, because in seasons of high prices for the 
staple it will be picked cleaner than when low prices prevail. This 
variation was illustrated in 1921 and 1922. The infestation on the 
Tlahualilo plantation, as shown in Table 18, was equally as high in 
1922 as it was in 1921, but the percentage of nonpickable cotton on 
this plantation (No. 31), as shown in Table 17, was 16.1 for 1921 
and 9.96 for 1922 (taking the average of the irrigated and unirri- 
gated fields). About the only explanation for this great difference 
is that the cotton was more closely picked in the latter season, a 
greater percentage of the severely damaged cotton being gathered 
and less "nonpickable" cotton left in the field. The price of picking 
at the end of the season and the price of low-grade cotton apparently 
substantiate this theory. The lowest grade of cotton (good ordinary) 
sold for 10 cents per pound during the 1921 season and for 15 cents 
per pound (Mexico City prices) during the 1922 season. At the 
same time the highest price paid for picking at the end of the season 
was 4 cents per kilo in 1921 and 6 cents per kilo in 1922. In this 
connection is presented Figure 9 to show the relation between non- 
pickable cotton and the price of cotton. 
Table 18. — Progress of infestation of green bolls, Tlahualilo plantation, 1921 and 
Month 
Week 
Percentage of bolls 
infested 
Number of worms 
per boll 
1921 
1922 
1921 
1922 
Third 
22.6 
7.3 
5.2 
4.9 
16.3 
15.8 
27.6 
31.1 
59.0 
84.1 
99.3 
99.9 
100 
100 
100 
100 
100 
100 
100 
99.2 
100 
100 
100 
0.22 
Fourth 
.08 
July .. 
First... 
.06 
Second.. .. 
17 
29 
32.1 
34.3 
43.7 
68.3 
87.9 
96.4 
95.5 
99.1 
99.3 
100 
100 
100 
100 
0.19 
.45 
.48 
.54 
.72 
1.57 
2.46 
3.42 
4.03 
4.36 
5.25 
5.82 
5.84 
6.98 
4.05 
.06 
Third 
;23 
Fourth 
.20 
First. .. 
.37 
.48 
Third 
1.05 
Fourth 
2.47 
Fifth . 
5.13 
September. . 
First 
6.48 
Second . . 
7.15 
Third 
7.16 
Fourth 
6.13 
October 
First .- 
8.57 
Second 
7.48 
Third 
5.87 
Fourth 
4.97 
First 
4.42 
3.16 
Third 
5.26 
Fourth... 
5.62 
