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



In general, it may be said that larvae will live in bolls submerged 

 in water or floating on the surface of the water till the bolls them- 

 selves are thoroughly rotten. This may be a week or more, depend- 

 ing upon the condition of the bolls. The old dried bolls and larvae 

 webbed up in bits of rubbish are particularly likely to carry an infes- 

 tation a long distance, for they float more readily than green bolls. 

 One of the large plantations was considering dividing their property 

 into zones which would be planted in cotton only every third or 

 fourth year in order to reduce the damage by the pink bollworm, but 

 the danger of reinfestation by irrigation water was considered so great 

 that it was not adopted. 



NATURAL CONTROL. 



From the data collected in 1918 and 1919, it is concluded that the 

 maximum infestation and the maximum damage to the cotton of 

 the Laguna have been reached by this time, except for slight yearly 

 variations due to climatic conditions which may have some effect 

 on the development of the pink bollworm and its attack on the 

 cotton. It is the belief of the plantation owners that the damage 

 or loss to the crop has remained about the same since 1916, or that 

 the maximum had been reached at the end of five years from the time 

 of introduction. 



MORTALITY OF NEWLY -HATCHED LARV,£. 



It has been shown in Table III that 47.1 per cent of the pink 

 bollworm eggs are not deposited on the squares or bolls. The larvae 

 from these eggs must crawl some distance before reaching food. In 

 this migration they are readily attacked by insect enemies, are ex- 

 posed to the hot sun, become weakened and exhausted, and event- 

 ually may succumb to starvation. It is thought that very few or 

 possibly none of the larvae from this 47.1 per cent of the eggs ever 

 enter the squares or bolls. Many of the larvae from the remaining 

 52.9 per cent of the eggs deposited on suitable parts of the plant 

 never succeed in entering the bolls or squares either. To determine 

 what percentage of the larvae hatching from eggs deposited on the 

 plants fail to enter the bolls or squares, five plants were examined. 

 These records were carefully made. Every part of the plant was 

 closely examined with a hand lens for eggs and eggshells. The larvae, 

 pupae, and exit holes were also carefully counted and the mortality 

 rate calculated from the number of eggshells found on the plants 

 and the total infestation of the plants. The results are given in 

 Table XIX. 



