53 
Journal of Agricultural Research 
Vol. XIV, No. i 
early fall and late spring, but thus far experiments have proved these of 
minor importance in connection with spinach-blight. 
(13) Differences in the habits of the aphids, however, cause Macro- 
siphum solanifolii to be the more important agent in the dissemination 
of the disease. Both aphids infest many species of plants. Experiments 
to determine whether any of these may constitute alternate hosts for 
the inciting factor of spinach-blight are not completed. 
(14) Direct transfers of virus-bearing aphids to healthy plants pro¬ 
duced infections of spinach-blight. * 
(15) Inoculation with the juice of crushed virus-bearing aphids pro¬ 
duced infections of blight. 
(16) Transfers of aphids which had not previously fed on diseased 
material produced infections of blight in a few cases. 
(17) Inoculations with the juice of lettuce, eggplant, peppers, and 
potato, used as food for the aphids, did not produce infections. 
(18) Blighted plants collected from various local farms and from 
blighted areas and individual diseased plants proved to be due to similar 
virus in all cases. 
(19) Virus-bearing aphids produced infections in healthy plants when 
allowed to feed on them for two minutes. 
(20) The infectivity is greater with adult aphids than with those 
which are immature, and the incubation period of the disease produced 
by the adults is materially less than when the disease is produced by the 
immature forms. 
(21) Aphids have the ability to carry infection to several healthy 
plants after leaving the diseased host. 
(22) Supposedly non-virus-bearing aphids were found to cause infec¬ 
tions of blight when transferred to healthy spinach. Aphids from 
Louisiana, Alabama, Florida, and Colorado when transferred to healthy 
spinach did not cause infections of spinach-blight unless they had pre¬ 
viously been allowed to feed on diseased spinach. Inoculations with the 
juice of crushed aphids from other States yielded similar results. 
(23) Non-virus-bearing aphids must remain on diseased plants for 5 
minutes to 14 hours to become carriers of infection. 
(24) Virus-bearing aphids do not lose their ability to transmit the 
causal entity of spinach-blight during the process of molting. 
(25) Infections were obtained with the offspring of virus-bearing aphids 
which had not previously partaken of food. 
(26) The infectious entity of spinach-blight was found to be trans¬ 
mitted by virus-bearing adult aphids to their offspring. It was also 
found that although aphids were reared on lettuce for four consecutive 
generations, yet a few of the fourth generation were virus bearers and 
produced infections when they were transferred to healthy spinach. 
These results show similarity to certain animal diseases caused by virus 
and transmitted by insects or ticks. 
