July x, 1918 
True Nature of Spinach-Blight 
35 
infected through the agency of the aphids placed upon them. The 
insects were confined on these plants for about five weeks during which 
time approximately four generations of first-born young were produced. 
This gave a large supply of supposedly nonvirus-carrying local aphids 
for use in making the transfers to healthy plants, and these insects and 
their offspring are referred to hereafter as the “Norfolk, Va., strain.” 
The mean temperature in the cages in which the aphids were confined 
was 76° F., with a relative humidity varying from 55 to 95 per cent. 
The results of the transfers are given in Table VIII. 
Table VIII .—Transfers of strains of supposedly non-virus-bearing aphids obtained from 
various States in comparison with the transfers of the local ( Norfolk , Va.) supposedly 
non-virus-bearing strain 
Species used. 
Source of insect. 
Previous 
food 
plant of 
insect. 
Num¬ 
ber of 
plants 
inocu¬ 
lated. 
Length 
of time 
insects 
were 
on 
plant 
Num¬ 
ber of 
plants 
in¬ 
fected. 
Aver¬ 
age 
length 
of in¬ 
cuba¬ 
tion. 
Num¬ 
ber of 
insects 
placed 
on 
each 
plant. 
Hours. 
Days. 
Macrosiphum solani- 
Norfolk, Va. 
Lettuce.. 
7 6 
48 
2 
28 
5 
folii. 
Rhopalosiphum persi- 
5 2 
48 
3 
2 7 - 3 
5 
cae. 
Macrosiphum solani- 
Eggplant 
24 
48 
2 
3 1 
2 
folii. 
Rhopalosiphum persi- 
.do. 
27 
48 
1 
34 
2 
cae. 
Macrosiphum solani- 
Spinach . 
a 500 
48 
39 
2 8. 4 
°2 
folii. 
Rhopalosiphum persi- 
.do. 
a 500 
48 
27 
32. 1 
a 2 
cae. 
Macrosiphum solani- 
Auburn, Ala. .. 
Lettuce . 
100 
48 
0 
2 
folii. 
Do . 
.do.. 
Spinach . 
100 
48 
0 
2 
Do. 
.do. 
Eggplant 
20 
48 
0 
2 
Rhopalosiphum persi- 
Baton Rouge, 
Pepper... 
SO 
48 
0 
2 
cae. 
La. 
Do. 
.do... 
Spinach . 
100 
48 
0 
2 
Do. 
Fort Collins, 
Peach.... 
20 
48 
0 
2 
Colo. 
Do. 
.do. 
Spinach . 
sO 
48 
0 
2 
Do. 
Gainesville, Fla. 
...do. 
40 
48. 
0 
2 
a Approximately. 
To 76 healthy spinach plants were transferred 400 of Macrosiphum 
solanifolii (Norfolk, Va., strain) which had previously been feeding on 
lettuce. The insects remained on the plants for 48 hours. Two of the 
spinach seedlings developed positive symptoms of blight in an average 
time of 28 days. About 250 individuals of Rhopalosiphum persicae (Nor¬ 
folk, Va., strain) which had previously been feeding on lettuce were trans¬ 
ferred to 52 healthy spinach seedlings, on which they were allowed to feed 
for 48 hours. Three of the spinach plants developed symptoms of blight 
in an average time of 27.3 days. Fifty of Macrosiphum solanifolii (Nor- 
