16 Journal of Agricultural Research voi. xiv, No. r 
EARLY FIELD EXPERIMENTS 1 ON THE INSECT TRANSMISSION OF 
SPINACH-BLIGHT, 1916-17 
The following data were collected from experiments performed in 
December, 1916, and January, 1917. The plants used in the experi¬ 
ments had been growing in large field cages for about three weeks 
previous to the time the inoculations were made. Large-sized lantern 
globes (PI. 10, A) were used to cover the plants during the 48-hour 
period which the aphids were allowed to remain on them. Adult 
apterous females were used in the transfers of aphids from the diseased 
to healthy plants. 
DIRECT TRANSFERS OF APHIDS FROM DISEASED TO HEALTHY PLANTS 
Series i 
Inoculations with Macrosiphum solanifolii. —Three plants in a 
field cage were selected and on the first were placed 10, on the second 
10, and on the third 20 individuals of M. solanifolii which had previously 
been feeding on diseased spinach. Positive symptoms of blight devel¬ 
oped on all three plants in 22, 17, and 22 days, respectively. The mean 
temperature inside the cages for the 22 days of the incubation period 
was 45 0 P. Outside the cages the mean temperature was 42 °. 
Inoculations with Rhopalosiphum persicae. —Another series of 
three healthy plants were inoculated by placing on them 10, 20, and 
10 individuals of R . persicae , respectively, from diseased plants. The 
typical mottling and malformations due to the disease appeared on all 
three of the plants 22, 29, and 22 days after the transfers were made. 
This experiment was conducted in the same cage as the first. No 
disease appeared on four untreated plants used as controls. 
Series 2 
Series 2 was started in January, 1917, and the results are shown in 
Table I. On January 17 thirty adults of Macrosiphum solanifolii which 
had been feeding on lettuce were placed on plant 1 of series 1, and 30 
adults of Rhopalosiphum persicae were placed on plant 4 of the same 
series. The aphids were allowed to feed for three days on these plants 
before the transfers were made. Individuals of M. solanifolii from 
diseased plant 1 were placed on three healthy plants. After feeding 
for 48 hours the aphids were removed. Positive symptoms of the 
disease developed in three of the plants 16, 16, and 23 days after inocu¬ 
lation. Three plants were inoculated by needle pricks with virus taken 
from plant 1. All three plants gave positive symptoms of the disease 
on the sixteenth day. Ten adults of M. solanifolii bom and reared on 
lettuce (Lactuca saliva) were placed on each of three healthy spinach 
1 During the summer of 1916 cooperative experiments were planned between the Entomologist of the 
Virginia Truck Experiment Station and Mr. D. E. Fink, of the Office of Truck Crop Insect Investiga¬ 
tions of the Bureau of Entomology. This work was started in the fall of 1916 on a spinach field on the 
Station farm. Successful transmissions of blight from diseased to healthy plants were obtained, and 
some data relative to the character of spinach blight collected. 
