THE POTATO TUBER MOTH. 
21 
METAMORPHOSES. 
The instars of the insect show the greatest irregularity, even where 
conditions as regards food and temperature are kept as nearly uni- 
form as possible. In determining the molting periods, a large num- 
ber of larvae, hatched on the same day, were placed on tubers and on 
each succeeding day the larvae were dissected from a tuber and pre- 
served in formalin. For the first two days the larvae were of approxi- 
mately the same size, but from the time of the first molt the greatest 
variation was noticeable; when some had reached the last instar 
others hatched on the same day and feeding on the same tuber were 
only half grown . 
This variation was also very noticeable in the life-history work. 
Where the first mature larvae appeared in 18 days, there were mature 
larvae leaving the tuber for the succeeding 6 days. Table 1 shows 
the variation in the length of the larval period with larvae from 
the same egg masses. 
Table 1.— Length of larval stage of the potato tuber moth with larvse from the same egg 
masses. 
Eggs hatched. 
Number 
of 
mature 
larvse. 
Dates between which they 
appeared. 
Number 
of days 
in emer- 
gence 
period. 
Nov 5 * 
1913. 
41 
8 
7 
11 
67 
23 
18 
47 
20 
38 
44 
19 
Dec. 16 and Jan. 4 
19 
Dec 3 
Feb. 3 and Feb. 21 
18 
Jan. 2 
1914. 
Mar. 2 and Mar. 28 
26 
Feb. 2 
Mar. 16 and Apr. 4 
19 
Mar. 19 
Apr. 21 and May 2 
12 
May 1 and May 12 
11 
June 2 and June 10 
8 
July 6 and July 14 
8 
July 5 
July 21 and July 27 
6 
Aug. 18 and Aug. 23 
Sept. 1 
Sept. 21 and Sept. 30 
Nov. 3 and Nov. 16 
9 
Oct. 4 
13 
As has been suggested, the rapidity of growth of the larva seems 
not to be influenced by the amount of food. Larvae developing 
in leaves, stems, or petioles, grew more rapidly than those in the 
tubers. In these experiments the larvae were kept on potted plants 
indoors, and those in tubers were placed in a breeding jar beside the 
plant. The experiments were carried on under the same temperature, 
but the larvae in the leaves were more exposed to changes in tem- 
perature, and whether the greatest difference in the time of develop- 
ment was caused by a variation in temperature or a difference in the 
character of the food, it would behard to determine. It seems probable, 
however, that the larvae in the potato tops had the most succulent 
food, and that this made some difference in the time of development. 
The results of the experiments are shown in Table 2. „ 
