PINK BOL.LWORM OF COTTON" IN MEXICO. 13 



on the sides of the sack. The old flowers under the plants did not 

 seem to be more favored than other bits of rubbish. 



The duration of the pupal stage of summer larvae from 150 records 

 ranges from 6 to 14 days. There is considerable variation among 

 the individual pupae, some requiring 1 to 2 days more than others 

 which pupated on the same night. 



Table IV summarizes over 300 complete records of the various 

 stages of the pink bollworm at Lerdo, Durango, Mexico, during 1918 

 and 1919. 



Table IV. — Duration in days of summer stages of P. gossypiella. 



Average 



Egg stage 4. G 



Larval instars: 



First 2-3 



Second , 3-4 



Third 3-4 



Fourth 4-5 



Total average 13. 3 



Pupal stage 9. 3 



Preoviposition period 3.8 



Total period from egg to egg 31. 



RESTING LARVAE. 



In the preceding part the development of the different summer 

 stages of the pink bollworm has been discussed. There is still 

 another important phase of the life history — the long-cycle or resting 

 larvae. It is in this stage that the species passes the winter when no 

 food is available or when conditions are adverse in any way. It is 

 also in this stage that the greatest dispersal by man takes place and 

 only in this stage that any known control measures can be used. 



Beginning some time in August, when the temperature is still high 

 and there is yet plenty of food available, some of the larvae upon 

 reaching maturity do not pupate at once, but remain wherever they 

 are as full-fed larvae. These larvae are identical in form with those 

 that pupate and can not be distinguished from them. What causes 

 some larvae to do this and others to pupate as usual when reared 

 under the same conditions is not known, but Willcocks (7) suggests 

 it is probably some instinct inherited from the time when in its orig- 

 inal natural habitat there were no food plants available to sustain 

 the species over a long period of time. In November and December, 

 when the temperature is lower and no food is available, all of the 

 larvae develop this tendency and it is the exception rather than the 

 rule for them to pupate. Thus in the Laguna this resting habit 

 seems to be a combination of estivation and hibernation, for it begins 

 while food is still available and the temperature high. In this sec- 

 tion the average frost date is about November 20, and moths emerg- 



