56 
Journal of Agricultural Research 
Vol. XXI, No. I 
GREENHOUSE EXPERIMENTS WITH INSECT CAGES 
During the winter of 1919-20, tubers from healthy Irish Cobbler 
potato plants were split in two and the halves planted in separate pots 
in the greenhouse at Washington, D. C. When the plants from these 
half tubers had reached a height of a few centimeters, some of them were 
inoculated by means of spinach aphids (Myzus persicae Sulz.), 1 which 
were transferred to the leaves after having been brushed from leafroll 
plants of the same variety into a wide-mouthed bottle. The aphids 
were allowed to feed for a few weeks before being killed with tobacco 
fumes. In each case the control plant from the corresponding half of 
the same tuber was grown under similar conditions and remained healthy. 
Additional data regarding these inoculations are given in Table IV. 
Table IV .—Leafroll inoculations by means of aphids 
Inoculated plants. 
Plant 
No. 
Inoculation. 
Date of 
Date of 
first 
symp¬ 
tom. 
Later obser¬ 
vations. 
Control plants. 
Date. 
Number 
Height 
cage. 
fumiga¬ 
tion. 
of aphids. 
of stalks. 
332a 
1920. 
Feb. 9 
About 50.. 
Cm. 
3 to 6 
Present to 
Mar. 5. 
Mar. 5 
Mar. s 
Apr. 2, se¬ 
vere leaf- 
332b, not caged 
or fed upon by 
roll. 
aphids. 
340a 
35 °a 
35 ia 
353 b 
Feb. 19 
About 100. 
5 to 8 
Present... 
Mar. 10 
Mar. 19 
.do. 
340b, like 332b. 
Feb. 24 
.do.. .. 
Mar. 17 
.. .do.. .. 
. .do.. .. 
350b, like 332b. 
...do. 
4 
.. .do. 
...do.... 
.do. 
351b, like 332b. 
4 
. do. 
... do.... 
...do.... 
.do. 
353a, about 100 
aphids from 
mustard Mar. 
13, when 4 cm. 
high. 
352b 
Mar. 2 
.. .do. 
4 
.. .do. 
...do.... 
Mar. 31 
Apr. 13, se¬ 
vere leaf- 
352a, like 332b. 
roll. 
355 a 
359 a 
...do.... 
.. .do. 
4 
.. .do. 
...do.... 
...do.... 
.do. 
355b, like 332b. 
...do.. .. 
.. .do. 
...do.. .. 
.do. 
359b, like 332b. 
356a, like 353a. 
From the data presented in Table IV it is apparent that the first 
symptom was noted from 24 to 29 days after inoculation. This consisted 
of a slight rolling of the lower leaves. Later this and other characteristic 
leafroll symptoms became severe, consisting of pronounced rolling and 
stiffness of the lower leaves, rolling in many cases of the majority of the 
upper leaves, slight marginal reddish discoloration of many leaves, and 
rigidity of the whole plant. On half the plants the aphids were killed 
from 9 to 14 days before the first symptoms appeared and in any case 
from 23 to 27 days before the symptoms were noted as being severe. 
Moreover, the control plants which were treated with nonvirulent aphids 
were still free from leafroll when last observed on April 15, so that aphids 
alone could not be considered as the cause of the leafroll symptoms. 
1 Identified by Dr. A. C. Baker, Entomologist, Deciduous-Fruit Insect Investigations, Bureau of Ento¬ 
mology, United States Department of Agriculture. 
