PINK BOLLWORM OF COTTON IN MEXICO. 17 



is cut just prior to pupation and not when the seeds are first webbed 

 together. Often the end of the pupal shell is seen protruding from, 

 the seeds through this opening. 



When pupation occurs in old bolls of cotton a favorite method is 

 to make a slight depression in the lint and pupate between the cot- 

 ton and boll. Where hibernation has been in the fields larvae may 

 leave the bolls and pupate in the ground. On March 14, 1919, li 

 square yards of soil in the corral at Lerdo, where many bolls were 

 lying around, were examined. Four live larvae and one dead one, 

 together with one live pupa and several empty pupal cases, were 

 found. All were near the surface, one larva being under a piece 

 of trash and the others an inch or so down. All the larvae and 

 the live pupa had light cocoons arid seemed to have gone into the 

 soil for pupation rather than hibernation. In the case of the old 

 pupal skins it could not be determined whether they came from 

 hibernating larvae or were left over from the previous summer. 



The duration of the pupal stage from 250 resting larvae ranged 

 from 8 to 26 days, with an average of 10.3 days. This is an average 

 of 1 day more than for the summer larvae, due to the fact that pup- 

 ation took place during the colder months. There is considerable 

 individual variation in the length of pupae formed at the same time, 

 but this occurs in pupae from summer larvae as well as from resting 

 larvae. The pupae from which male moths emerged required an 

 average of one-half day more than those from which females emerged, 

 the males requiring 10.5 days and the females 10 days. 



Time of Emergence from Resting Larvae. 



A few moths may emerge throughout the year in the Laguna. 

 When work was first begun in the early part of February, 1918, 

 freshly formed pupae were found among seed at the seed warehouses. 

 During the month of March, 1918, there emerged 23.5 per cent of all 

 the moths which emerged during the year from larvae coUected in 

 seed in February and removed to the laboratory. Emergence con- 

 tinued till August, when all of the larvae had died or emerged, the 

 maximum being reached in May. Pupae were formed from larvae 

 collected in the summer and fall of 1918 throughout the fall and 

 into January, 1919, thus completing the cycle of pupation for every 

 month in the year. The pupal period is greatly retarded during the 

 cold months, but this does not prevent emergence on warm days. 

 Table VII shows the monthly emergence of moths from resting 

 larvae for 1918 and 1919. 



11696°— 21— Bull. 918 3 



