98 BULLETIN 1476, U. S. DEPARTMENT OF AGRICULTURE 
wintering larvae found in the field revealed an entire absence of 
solid food, and when these larvae were isolated from any boring 
medium whatever and supplied with proper moisture conditions, 
they pupated and emerged as normal adults. 
Repeated experiments have been performed in which overwintering 
larvae were confined during April and May in small cages with green 
succulent stalks of rhubarb, celery, Rumex, and Polygonum. None 
of these individuals fed upon or entered these plants, although 
rhubarb, celery, Rumex, and Polygonum are preferred hosts of the 
active feeding larvae during the summer. 
Field examinations during April and May of rhubarb, spinach, 
and early spring weeds growing closely adjacent to plant remnants 
containing overwintering larvae failed to show any infestation in 
these plants by such larvae. 
DURATION OF LARVAL LIFE WITHOUT FOOD 
The larvae of P. nubilalis are capable of maintaining life without 
food for a considerable period of time during their active develop- 
ment. This is especially true of larvae in the later instars. By iso- 
lating, in individual cages, a large series of first-generation larvae 
of each instar, it was determined that the average duration of life 
without food for the first instar was 1.95 days, second instar 5.5 
days, third instar 6.7 days, fourth instar 8.1 ofays, fifth instar 22.8 
days, and for the sixth instar 31.3 days. In this series newly hatched 
larvae were used for the first instar and newly molted larvae for each 
of the subsequent instars. Pieces of damp blotting paper provided 
suitable moisture conditions in each cage. 
MOLTING 
When tunneling inside its host plant, the larva molts within its 
tunnel near the last feeding place. Where the larva is feeding upon 
or close to the surface of its host plant, as frequently occurs during 
the early instars, molting usually takes place inside a thin silken web 
with which the larva surrounds itself for protection or concealment. 
Certain individuals in all instars have also been observed molting 
on the outside of the host plant without any other protection than 
that afforded by fragments of frass or a few strands of silk spun by 
the larva previous to molting. 
LARVAL MIGRATION 
The migration of Pyrausta mibilalis larvae from one part of the 
host plant to another part of the same plant, or to near-by plants, 
has already been discussed. In addition to this very localized migra- 
tion, the larvae, especially in their later instars, frequently leave 
their host plants when such plants are disturbed, or when such hosts 
become unsuitable for food or shelter through decay or as a result 
of the drying out of the plant tissues. This migration is especially 
likely to occur (1) where infested cornstalks are being collected in 
the fields; (2) where such stalks are left in piles of " stacks " in the 
field, in the barnyard or under shelter, with the consequent decay 
through excessive moisture, or the drying out of the plants when 
protected from rain and snow; (3) when badly infested plants col- 
