PINK BOLLWORM OF COTTON IN MEXICO. 
25 
discolor the lint. Just as soon as the bolls are formed they may be 
attacked by the larvae working downward from the flower, but 
usually they are not attacked till one-half to three-fourths grown. 
The damage to the individual boll is greater the earlier it is attacked. 
In case the larva enters when the boll is very young, that is, one- 
half grown or less, the boll is usually completely destroyed. But 
when a boll is not attacked until it is about half grown an infesta- 
tion by a larva or even several larvae does not necessarily prevent 
the boll from opening and producing some pickable cotton. The 
cotton from infested bolls is of an inferior grade, the lint usually 
being short, hard, and kinky. The portion of the boll actually con- 
sumed by the larva may be comparatively small, but the damage 
caused by the feeding habits and presence of larvae in a boll amounts 
to a considerable percentage loss to the crop. The irritation pro- 
duced by the presence of a larva often causes proliferation to take 
place; and upon entering and leaving the boll the larvae provide a 
•means for the entrance of air and water, thereby causing decompo- 
sition in the green bolls. 
RELATION OF AMOUNT OF DAMAGE TO INCREASE OF INFESTATION. 
It has been estimated that the natural winter mortality of all 
insects is about 95 per cent or more. In addition to this, the number 
of pink bollworms in the cotton fields of the Laguna district is further 
reduced by the irrigation methods, fall burning of plants, and the 
grazing of the fields by cattle, goats, etc. It is obvious that at the 
beginning of the crop the infestation, even where it was general the 
previous year, would be very light, but as the number of larvae in 
the field increases the amount of damage becomes greater. 
The pink bollworm attack is not similar to that of other insects 
like the cotton leafworm, Alabama argillacea Hiibn., or bollworm, 
Chloridea obsoleta Fab., which practically ruin a crop overnight, but 
is more of a gradual, built-up attack, starting in the beginning of 
the crop with practically a negligible infestation and culminating 
with 100 per cent of the bolls infested with from 4 to 10 larvae in 
every boll. Table XI shows the rate of monthly increase of larvae 
in several average fields of the Laguna. 
Table XI. — Progress of infestation by larvx of the pink bollworm; number of larvae per 
100 bolls. 
Plantation. 
Month. 
Hormi- 
guero. 
Alvia. 
LaCon- 
cha. 
San Isi- 
clera. 
Zaragosa. 
Rosas. 
Barce- 
lona. 
Average. 
August..., 2.6 
September 103.0 
October 1 710.0 
November ! T20. 
15.3 
128.7 
694.0 
790.0 
5.0 
93.5 
585.2 
668.0 
5.2 
62.7 
748.0 
638.0 
32.6 
312.0 
773. 
33.6 
210.7 
807.4 
864.0 
17.6 
188.0 
496.6 
464.0 
15.9 
156.0 
662.9 
724.0 
11696°— 21— Bull. 918- 
