10 BULLETIN 918, U. S. DEPARTMENT OF AGRICULTURE. 



LARVA. 



Newly-Hatched Larv.e. 



The newly-hatched larvae are creamy white, with dark-brown 

 head and thoracic shield and long, prominent, dark seta? showing 

 very plainly. They are a little less than 1 mm. in length and grad- 

 ually taper from the head, having thus a slight wedge-shaped appear- 

 ance. In this stage the larva? are very active. Under laboratory- 

 conditions they are very restless and crawl rapidly from place to 

 place before entering a square or boll. Many larva? continue crawl- 

 ing around for 24 hours or more until they become so weakened that 

 they are not able to cut their way into the squares or bolls. It was 

 often observed that most of the larva? which succeeded in entering 

 the food provided for them did so the day they were hatched. It is 

 not known to what extent this wandering around takes place under 

 natural conditions. Larva? are found crawling over the plants, but 

 they always seem restless and ill at ease. This probably does not 

 take place normally to any great degree, except in the case of larva? 

 from eggs laid on other parts of the plant than the squares and bolls. 



Larvae Entering Bolls. 



The larva? do not seem to have any preference as to where the boll 

 is entered. Sometimes a light netlike web is spun and the entrance 

 is made underneath it. At other times the entrance is made with 

 no protection whatever. The larva? cut the carpel away, throwing 

 the fragments outside, very little if any being consumed. The time 

 required for the larva? to enter may vary with the age of the boll, 

 but it usually takes them from 20 to 40 minutes to become com- 

 pletely hidden. If the boll is examined soon after they have entered, 

 the holes are easily located by the surrounding frass, and although 

 minute, can be seen with the naked eye. After 2 or 3 days the frass 

 is blown away by the wind or removed by other agents and the 

 holes close up, leaving only brownish spots which are hard to dif- 

 ferentiate from other discolorations on the boll. Then they can 

 only be detected by a trained eye, and the only way to be certain a 

 boll is infested is to examine its interior. 



Larvae After Entering Bolls. 



After the boll has been entered the larva? become glassy white, 

 soft, and sluggish. The} 7 so closely resemble the watery lint at this 

 stage that they would be very easily overlooked, except for their 

 dark heads and thoracic shields, which show as black specks against 

 the lint. 



There are three molts, conrpleting four larval instars or stages. 

 The first stage lasts about 2 days; the second and third, 3 to 4 days 

 each; and the fourth, 4 to 5 days,; thus the larval development is 



