36 
Journal of Agricultural Research 
VoL XIV, No i. 
folk, Va., strain) were transferred from eggplant to 24 healthy spinach 
seedlings. Two of the plants developed positive symptoms of blight in 
30 and 33 days, respectively. Fifty of Rhopalosiphum persicae (Norfolk, 
Va., strain) which had been feeding on eggplant were transferred to 27 
healthy spinach seedlings. One infection resulted, and the first positive 
symptoms developed on the thirty-fourth day. 
In one of the large field cages seed was sown broadcast, and about 500 
healthy plants were thus obtained. One thousand individuals of Macro¬ 
siphum solanifolii (Norfolk, Va., strain) which had previously been feed¬ 
ing on spinach were transferred to the plants in this cage. At the end of 
of the 48-hour period that the aphids were allowed to remain on the plants, 
the cages were fumigated on three consecutive days with nicotine. In 
this way all the aphids were destroyed. Thirty-nine cases of blight de¬ 
veloped on the plants in an average time of 28.4 days. About 1,000 indi¬ 
viduals of Rhopalosiphum persicae (Norfolk, Va., strain) were transferred 
to a second large field cage in which were growing approximately 500 
spinach seedlings. After the aphids had remained on the plants for 48 
hours, they in turn were destroyed by three successive fumigations. 
Twenty-seven of the plants in this cage became infected with blight. The 
first positive symptoms appeared in an average time of 32.1 days. Two 
hundred of Macrosiphum solanifolii (Auburn, Ala., strain) from healthy 
spinach were transferred to a cage containing 100 healthy spinach seed¬ 
lings. No infections were obtained. Forty of Macrosiphum solanifolii 
(Auburn, Ala., strain) were transferred from eggplant to 20 healthy spin¬ 
ach seedlings. No infections were obtained. In a similar manner the 
following transfers were made. The insects remained on the plants for 48 
hours in each case before they were destroyed. One hundred of Rhopalo¬ 
siphum persicae (Baton Rouge, La., strain) from peppers, were transferred 
to 50 healthy spinach seedlings. Two hundred of Rhopalosiphum persicae 
(Baton Rouge, La., strain) were transferred from healthy spinach to 
healthy spinach seedlings. Forty of Rhopalosiphum persicae (Fort Col¬ 
lins, Colo., strain) were transferred from peach to 20 healthy spinach 
seedlings. One hundred of Rhopalosiphum persicae (Fort Collins, Colo., 
strain) were transferred from healthy spinach to 50 healthy spinach seed¬ 
lings. Eighty of Rhopalosiphum persicae (Gainesville, Fla., strain) were 
transferred from healthy spinach to 40 healthy seedlings. No infections 
were obtained as a result of any of the above transfers, and the seedling 
plants remained healthy in every case until the close of the experiments. 
A series of healthy spinach plants were inoculated with the juice of the 
lettuce, eggplant, spinach, and pepper plants, upon which the aphids had 
been feeding previous to their transference to the healthy spinach seed¬ 
lings in the experiment. No infections resulted from these inoculations, 
except from the inoculations with the juice of the spinach plants on 
which the Norfolk strain had been feeding, in which case 2 positive 
infections resulted from 10 inoculations. 
