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 Hubn., or bollworm, 

 CMoridea 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 larvae of the pink bollworm; number of larvae -per 



100 bolls. 





Plantation. 





Month. 



Hormi- 

 guero. 



Alvia. 



LaCon- 

 cha. 



San Isi- 

 dera. 



Zaragosa. 



Rosas. 



Barce- 

 lona. 



Average. 



August 



2.6 

 103.0 

 710.0 

 C20.0 



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 

 773.0 



33.6 

 210.7 

 807.4 

 864.0 



17.6 

 188.0 

 496.6 

 464.0 



15.9 

 156 





662 9 



November 



724 









11696°— 21— Bull. 918- 



