July i, 1918 
Trite Nature of Spinach-Blight 
17 
seedlings. After remaining on the plants for 48 hours, the aphids 
were removed. No cases of blight had developed at the time the experi¬ 
ment closed, 54 days after the transfers were made, thus indicating 
that the aphids from lettuce did not carry infection. Ten control 
plants which were untreated remained healthy. Ten adults of 
persicae taken from plant 4 were placed on three healthy spinach plants. 
All three developed blight on the sixteenth day. Three plants were 
inoculated by needle pricks with the virus from plant 4. Two of the 
plants developed positive symptoms of the disease on the fifteenth 
day. The third remained healthy until the experiment closed. Forty 
adult R. persicae , the offspring of individuals which had been feeding 
on lettuce for three generations, were distributed equally on four healthy 
spinach plants. They remained on these plants for a period of 48 hours 
and were then removed. One plant developed typical symptoms of 
blight 23 days after it was inoculated. The three remaining plants 
were still healthy when the experiment closed. Ten plants which were 
untreated and used as controls remained healthy. 
Table I .—Results of field experiments on the insect transmission of spinach-blight (series 
2), Norfolk, Va. } igiy 
Mean 
temper¬ 
ature 
in cages 
during 
incu¬ 
bation 
period. 
*F 
45 
43- 2 
45 
45 
45 
45 
45 
45 
45 
45 
43.2 
Source of diseased 
material. 
Method of trans¬ 
mission. 
Species of insect used. 
Incubation 
period. 
Plant 1, first series 
1916 experiments. 
.do. 
10 live aphids.... 
8 live aphids. 
Macrosiphum so- 
lanifolii. 
.do. 
Days. 
16 
16 
23 
16 
16 
16 
Healthy. 
... do .... 
.do. 
12 live aphids.... 
.do. 
Needle pricks with 
diseased tissue. 
.do. 
.do. 
.do. 
.do...... 
Controls untreated.. 
.... do. 
.do. 
... do .... 
Aphids reared for 
two generations 
on lettuce. 
.do. 
10 live aphids.... 
M. so lanifolii. 
.do... 
. . do .... 
.do. 
Healthy, 
do ,... 
.do... 
.do. 
.do. 
Plant 4, first series.. 
.do. 
Rhopalosiphum 
persicae . 
.do. 
16 
16 
16 
15 
*5 
Healthy. 
... do .... 
.do. 
.do. 
.do.... 
5 live aphids. 
.do. 
.do.... 
Needle pricks.... 
.do,. *. 
.do. 
.do. 
.do. 
Controls untreated.. 
.do. 
..do .... 
.do. 
.. do .... 
Aphids, third gener¬ 
ation, on lettuce. 
.do. 
10 live aphids.... 
.do. 
R. persicae. 
.do. 
23 
Healthy. 
.do. 
.do.. 
.do... 
.do. 
.do. 
.. .do .. .. 
Plant 
No. 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
14 
15 
16 
17 
18 
19 
20 
21 
22 
23 
24 
3 
57664°—18-2 
