THE GEAPE LEAEHOPPEB IN THE LAKE ERIE VALLEY. 
27 
record made of the date of each molt. During this operation the 
moisture was wiped from the inside of the watch glass. 
The period covered by these rearing experiments was from June 
22 to October 13. During this time 348 newly hatched nymphs were 
placed on grape leaves confined in cages similar to those just described. 
Many of the nymphs either died or escaped before they completed 
all of the nymph al stages. Nevertheless, complete records of the 
length of the five stages were secured for 114 nymphs. The greater 
number of fatalities occurred among the young nymphs during the 
early part of the rearing season before the leaf cage most suitable for 
the purpose was secured. After the double thickness of velvet was 
adopted fewer fatalities occurred. 
The lengths of the several stages for the different individuals 
show a great variation, but it will be noted by an examination of 
Table XI that the variation of the total length of the five stages for 
a number of nymphs hatching on the same date is not very great. 
Changes in temperature appear to be the important factor in deter- 
mining the length of time required to complete the entire nymphal 
period. 
In the last column of Table XI the average daily temperature 
for the entire nymphal period of each of the 114 nymphs is given. 
These average temperatures are computed from the average daily 
temperatures given in Table XII. The average daily temperatures 
given in Table XII are derived from daily readings of a maximum 
and minimum thermometer, located in the garden of the laboratory 
at North East, Pa., only a few yards distant from the grapevines 
bearing the individual cages in which the nymphs were reared. 
Table XI. — Length of each of the five nymphal stages of the grape leaf hopper for 114 
nymphs recorded from June 22 to October 13, 1912. 
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June 22 
June 28 
6 
June 30 
2 
July 4 
4 
July 7 
3 
July 11 
4 
19 
74. 90 
July 5 
July 9 
4 
July 10 
1 
July 13 
3 
July 16 
3 
July 25 
9 
20 
76.60 
July 9 
July 12 
3 
July 15 
3 
July 20 
5 
July 25 
5 
Aug. 8 
14 
30 
69.97 
Do... 
July 15 
6 
July 18 
3 
...do 
2 
...do 
5 
Aug. 7 
13 
29 
70.10 
Do... 
...do 
6 
July 17 
2 
July 21 
4 
July 28 
7 
Aug. 8 
11 
30 
69.97 
Do... 
July 12 
3 
July 15 
3 
July 20 
5 
Aug. 2 
13 
Aug. 12 
10 
34 
70.04 
Do... 
July 13 
4 
July 16 
3 
July 21 
5 
July 27 
6 
Aug. 9 
13 
31 
70.03 
Do... 
...do 
4 
July 17 
4 
July 19 
2 
July 25 
6 
Aug. 7 
13 
29 
70.01 
Do... 
...do 
4 
...do 
4 
July 21 
4 
July 28 
7 
Aug. 10 
13 
32 
70.11 
Do... 
...do 
4 
...do 
4 
July 19 
2 
...do 
9 
Aug. 9 
12 
31 
70.03 
Do... 
...do 
4 
...do 
4 
...do 
2 
...do 
9 
...do.... 
12 
31 
70.03 
Do... 
July 12 
3 
July 15 
3 
...do 
4 
July 25 
6 
Aug. 8 
14 
30 
69.97 
Do... 
July 13 
4 
July 17 
4 
July 21 
4 
July 27 
6 
...do 
12 
30 
69.97 
Do... 
July 14 
5 
July 18 
4 
July 23 
5 
July 29 
6 
Aug. 10 
12 
32 
70.12 
Do... 
July 13 
4 
July 16 
3 
July 21 
5 
July 28 
7 
Aug. 9 
12 
31 
70.03 
