14 BULLETIN 918, TJ. S. DEPARTMENT OF AGRICULTURE. 



ing after this date would as a rule find no suitable places for ovi- 

 position. 



When a larva prepares to go into the resting stage it remains in 

 the boll in which it has been feeding. Usually a tough, heavy co- 

 coon is spun either in the lint, in a single seed, or two seeds are fas- 

 tened together to form a "double seed." (PI. II, B.) The double 

 seed is formed by eating away part or all of the contents of the two 

 adjoining seeds and spinning a strong continuous cocoon inside the 

 cavities of the two seeds, which holds them firmly together and 

 makes them difficult to separate. 



Part of these seeds go through the gin and come out intact, and 

 finding double seed is sure evidence of pink-bollworm infestation. 



Often double seeds are formed in seed in different locks, the con- 

 necting cocoon running through the hole made in the partition wall. 

 This affords good protection for the larva, as it prevents the seed 

 from falling to the ground and being exposed to excessive moisture 

 and other agencies which are more detrimental to the larva on the 

 ground than on the plants. 



When the cocoon is spun in the lint or a single seed the larva lies 

 in a curled-up position and the cocoon is spun tightly around it, 

 forming a spherical compact mass. Similar cocoons are formed in 

 the ground or attached to any convenient object if larvae are removed 

 from seed or lint. The cocoon fits so closely and is so tough that it 

 is very difficult to remove without injuring the larva. It is very 

 hard to detect a larva inside a seed, and the only sure way to tell 

 whether the seed contains a larva is to examine the interior. Will- 

 cocks (7) in writing about Egyptian cottonseed, which has a smooth, 

 black coat and is not covered with lint, says the silken-covered en- 

 trance hole can usually be seen with a lens. This, however, does not 

 hold true for short-staple seed. 



Few data are available on the number and proportion of larvae 

 found in the lint and in the single and double seed. Samples of cot- 

 ton were hand-ginned and the number of larvae in single and double 

 seed determined, but unfortunately no record was kept of the num- 

 ber in the lint. It is possible that some of the larvae counted as in 

 single seeds in the first and second picking samples were in the lint, 

 but this did not occur in the samples of the third picking. It will 

 be noted that the sample for the third picking is from the 1918 crop 

 and had been stored for some time. At the time of examination a 

 considerable part of the larvae were dead, but this does not affect the 

 proportion found in the single and double seed, and while the figures 

 are not quite comparable, they at least give an idea of the number 

 of larvae present at different times. The number of larvae found in 

 the single and double seed for the different picks are given in Table V- 



