July i, 1918 
True Nature of Spinach-Blight 
39 
LENGTH OF TIME non-virus-bbaring aphids must rbmain on disbasbd 
PLANTS BBFORB THBY BBCOMB VIRUS BBARBRS 
As it was found that the offspring of aphids from Alabama, Louisiana, 
Colorado, and Florida did not produce blight infections when reared on 
lettuce, eggplant, or healthy spinach unless they had first fed on a blighted 
spinach plant, the following experiments were performed to determine 
the length of time that these aphids must remain on a diseased plant 
before they become virus bearers. Offspring of Macrosiphum solanifolii 
from Alabama and Rhopalosiphum persicae from Louisiana were placed on 
blighted spinach plants. The disease had been produced by means of 
needle-prick inoculations and the pathogenicity had been proved before 
the aphids were transferred to them. The results are presented in 
Table X. 
Table X .—Length of time non-virus-bearing aphids must remain on diseased plants 
before they become virus carriers 
Species. 
Length of time 
aphids remained 
on blighted plants. 
Number of 
plants 
inoculated. 
Number of 
plants 
infected. 
Average 
period 
of incu¬ 
bation. 
Macrosiphum solanifolii (Alabama)... 
Do. ... 
48 hours. 
IO 
0 
Days . 
18. I 
24 hours........ 
10 
y 
8 
17 . 2 
Do. 
14 hours. 
10 
10 
f 
18.7 
21. 3 
24 
Do. 
2 hours. 
IO 
6 
Do. 
10 minutes. 
IO 
2 
Control. 
48 hours. 
IO 
Rhopalosiphum persicae (Louisiana). . 
Do. 
24 hours. 
IO 
7 
6 
17 
i 7-5 
20 
14 hours. 
IO 
Do. 
2 hours. 
IO 
4 
Do. 
10 minutes. 
IO 
T 
Control. 
48 hours. 
IO 
After the aphids had remained on the diseased plants for 10 minutes, 
30 of Macrosiphum solanifolii (Auburn, Ala., strain) were removed and 
placed on ten 2 2-day-old spinach seedlings. The insects remained on the 
plants for 24 hours and were then killed by fumigation. Of the 10 plants 
thus inoculated 2 became infected, the positive symptoms appearing in an 
average time of 24 days. In a similar manner 10 healthy spinach 
seedlings were inoculated by transferring to them 30 of Rhopalosiphum 
persicae (Louisiana strain) which had previously been allowed to feed 
on the diseased plants for 10 minutes. No infections occurred. Thirty 
of M. solanifolii were removed after feeding on diseased plants for a 
period of two hours and placed on 10 healthy spinach. seedlings. Six 
infections resulted, the positive symptoms appearing in an average time of 
21.3 days. Ten plants were inoculated with R. persicae (Louisiana 
strain) which had been feeding on a diseased plant for two hours. Four 
plants became infected in an average time of 20 days. All of the 10 plants 
