PINK BOLLWORM 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 LARV.E. 
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- 
