THE POTATO TUBER MOTH. 23 
In the field, where the larvae were working on potato tops, the pupae 
were noted in the following places: (1) In curled dried leaves on the 
plant; (2) under clods and rubbish, and (3) protruding from old 
burrows in the stem. 
Under field conditions most of the pupae were found in the dried 
leaves which still clung to the potato plant. 
After the larva has completed its cocoon it spends a period varying 
from two days to a week or more before changing to the pupa. The 
larva becomes greenish all over and sometimes takes on a faint blue 
tinge. It also becomes much shortened and constricted at the seg- 
ments, and loses nearly all its activity. This stage varies very much 
with the temperature, being much shorter in summer than in winter. 
The larva is helpless at this time and can not move within its cocoon 
sufficiently to ward off the attacks of parasitic enemies. During 
this period the greatest amount of parasitism of the mature larva 
takes places. 
THE PUPA. 
As the time of pupation approaches, the skin on the dorsum of the 
anterior segments of the larva splits, and the pupa works the skin off 
in a short time. The cast skin occupies a small space in the posterior 
end of the cocoon. 
The pupa when newly formed is white with greenish markings. 
It soon begins to darken and hi a few hours' time is uniformly dark 
brown. When first formed it remains quiet until it becomes hard- 
ened, but is very sensitive and if disturbed turns itself around by 
moving the tip of its abdomen in a circle. The hooks at the tip of the 
abdomen are sometimes fastened in the cocoon, so that even if part 
of the anterior end of the cocoon is torn off, the pupa will not neces- 
sarily be dislodged. Just before emergence it is quite active and 
turns itself around quickly if disturbed. As the time for emergence 
approaches the pupa becomes still darker in color and is less active. 
The period of pupation varies greatly with the temperature and 
even when under constant temperature. Lots of pupae formed on 
the same day vary to such an extent that the last to emerge often 
requires twice as long as the first. Experiments undertaken to de- 
termine the influence of sex on the length of the pupal period gave 
entirely negative results, as both sexes were practically evenly divided 
at all periods of emergence. 
Extreme variations for the pupal period indicated 8 days for 
July and 56 days for December and January. Variations during 
one month include 12 days for the shortest and 29 days for the 
longest period. 
Even where the pupal stage is of the longest duration the ratio 
of this to the increased length of the other stages of the moth re- 
mains so nearly constant that it seems development within the 
