42 
Journal of Agricultural Research 
Vol. XIV, No. I 
adult aphids fed on the spinach for 7 days and were then retransferred 
to lettuce. On these plants they remained for 3 days, or until about 200 
first-generation young had been bom to each lot. The adults were re¬ 
moved, some being transferred to healthy plants for 48 hours. These 
were termed the “original parent aphids.” When the offspring reached 
maturity and had produced between 200 and 300 young, the first-genera¬ 
tion adults were removed and, as before, some were transferred to healthy 
plants. In like manner, as the second, third, and fourth generations 
matured, they were transferred to series of healthy spinach plants. Thus, 
inoculations were obtained from four generations representing three 
strains and two species of aphids. Two separate tests were conducted 
with each species: one in the insectary on potted plants and another in 
the field cages on plants grown under outdoor conditions. Five insects 
were placed on each plant and 10, 20, or 25 plants were used with each 
generation in each series. The results of this experiment are given in 
Table XI. 
Table XI .—Transmission of the infectious entity of spinach-blight by virus-bearing aphids 
to their offspring 
Species used. 
Generation. 
Num- 
N um¬ 
ber of 
insects 
per 
ber of 
plants 
inocu- 
Number of 
plants 
infected. 
plant. 
lated. 
Aver¬ 
age 
length 
of incu¬ 
bation 
period. 
Greenhouse series: 
Macrosiphum solanifolii 
(Norfolk, Va. } strain). 
M. solanifolii . 
Do. 
Do. 
Do... 
Outdoor series: 
Original parent 
aphids from dis¬ 
eased plants. 
First. 
Second.. 
Third.. 
Fourth.. 
5 25 
5 25 
5 25 
5 25 
5 25 
23 
Days. 
18. I 
8 
2 
2 
I 
24. 2 
33 
-34 
37 
M. solanifolii 
Do. 
Do. 
Do. 
Do. 
Greenhouse series: 
Rhopalosiphum persicae 
(Norfolk, Va., strain). 
Do. 
Do. 
Do. 
Do. 
Outdoor series: 
Original. 
First. 
Second. 
Third. 
Fourth. 
Original virus-bear¬ 
ing aphids. 
First. 
Second. 
Third. 
Fourth. 
5 
5 
5 
5 
5 
10 
10 
10 
10 
10 
5 25 
5 25 
5 25 
5 25 
5 25 
10 
2 
3 
1 
o 
22 
37 
34-3 
39 
o 
21 
17.4 
4 
2 
1 
o 
24. 2 
26 
24 
o 
R. persicae . 
Do. 
Do. 
Do. 
Do.. 
Greenhouse series: 
M. so lanifo Hi Auburn, 
(Ala., strain). 
Do. 
Do. 
Do. 
Do. 
Original 
First. ... 
Second. 
Third. .. 
Fourth. , 
Original 
First. ... 
Second. 
Third. .. 
Fourth.. 
S 25 
5 25 
5 25 
5 25 
5 25 
18 
2 
1 
2 
1 
21.3 
28 
37 
32 
35 
5 10 
9 17 
5 
5 
5 
5 
10 
10 
10 
10 
2 
Healthy. 
2 
1 
24 
32 
36 
