rere 7 > 
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THE ROUGH-HEADED CORN STALK-BEETLE 13 
5 to 8 weeks after hatching—usually this is about a week or 10 days 
before it is ready to enter the prepupa stage. 
DURATION OF THE LARVAL PERIOD 
The length of the larval period in the experimental series varied 
from 44 to 94 days. In the majority of cases, however, it falls be- 
tween 50 and 65 days, a fair average being about 57 days. Instances 
in which the duration of this stage was greater than this mostly. 
belong to those larvee which developed late in the season, when low 
temperatures retarded their growth. 
- The earliest date at which larve have been found at Tappahan- 
nock is June 19. This was in 1916, when a few were hatched from 
eges collected in the field on June 5. In the breeding experiments 
of 1915, larvee were still being hatched as late as November, but 
this was evidently abnormal, as there is no evidence that any are 
ever hatched in the field later than the first part of August. The 
latest date on which the young larve have been found in the field 
is August 12. This was in 1916, when two were obtained in the old 
pasture at Tappahannock. The latest date on which full-grown 
larvee have been observed in the field is November 2. This also was 
in 1916, when W. T. Emery recorded finding a few larve of what 
he supposed to be this species in the same pasture. These specimens 
were unfortunately lost before their specific identity could be fully 
established. As the early fall of 1916 was unseasonably cold, it is 
not unlikely that such an extension of the larval period as is in- 
dicated by Mr. Emery’s observation may have occurred. 
Although it is possible that the latest developing larve may, in 
some instances, fail to reach maturity before winter, there is no 
evidence that any ever survive until the following spring. Both 
field observations and experiments to test this possibility have given 
only negative evidence. At Charlottesville the larvee, each in its 
own box, were buried in a compost heap on the approach of winter, 
but when the boxes were dug out and examined in the spring all 
the larvee were dead. 
MOLTING 
Experiments to determine the number of molts and the duration 
of the periods between molts were madé at Charlottesville. Each 
larva upon hatching was transferred to a salve box, the bottom of 
which was covered. with a disk of moist blotting paper on which 
were placed a few particles of old cow manure, which had been 
previously fumigated with chloroform. ‘These experiments were 
begun August 14, 1915, and were continued throughout the fall and 
early winter. After September 25 the larve were kept indoors, 
where they were subjected to artificial heat. The mortality in these 
experiments was high, even after vegetable mold had been sub- 
stituted for the manure. Consequently only a very small propor- 
tion of the larve completed their development. 
Owing to the late date at which these experiments were begun 
the time intervals recorded between successive molts can have little 
significance as regards the duration of these intervals under field 
conditions. 
