October, ’20] FENTON AND HARTZELL: POTATO LEAFHOPPER 
407 
Table III. Incubation Period in the Insectary 
Brood 
Number of records 
Minimum 
Maximum 
Average 
1. 
109 
4 days 
10 days 
7\ days 
2. 
31 
4 days 
12 days 
7 days 
The greatest number of nymphs hatched during the morning, before 
the heat of the day. Certain conditions of temperature and humidity 
greatly influenced this, for hatching occurred at the same time through¬ 
out the whole field. During July this period generally came between 
8.30 and 9.30 a. m., but later in September, not until after 10. 
During the height of the egg-laying period, great numbers of nymphs 
w^ere continually hatching from a plant. Our records, based on care¬ 
fully made field counts, showed an average of 1,943 nymphs hatched 
from one plant during a ten weeks’ period from July 23 to October 3. 
During this time the percentage of egg parasitism was relatively high, 
so that this does not represent the total number of eggs deposited, 
which must have been considerably greater. This gives an idea of 
the population of leafhoppers one potato plant may support during a 
season. The possible number per acre would thus run above ten 
millions. 
These hatching records were obtained by a daily examination of six 
branches of potato plants and counting and removing the newly- 
hatched nymphs. This served as an index to the appearance and 
abundance of second generation young. August 6 hatching of second 
generation eggs was already taking place. This continued until frost 
in October, although at this time very few were found on the plants. 
It was noted that the greatest number of nymphs hatched out from 
August 20 to September 6, and that September 11 the number of 
nymphs hatching was greatly reduced. 
Length of Nymphal Life 
The average length of time spent in the nymphal stages for the first 
two was two days, for the third and fourth, three, and for the last, 
Table IV. Comparative Length of Nymphal Instars 
Stage 
Number of insects 
observed 
Minimum 
Maximum 
Average 
1. 
30 
2 
3 
2 
2. 
32 
1 
4 
2 
3. 
31 
1 
5 
3 
4. 
28 
1 
6 
3 
5. 
33 
3 
8 
4 
Total. 
154 
8 
26 
14 
