THE MOSAIC DISEASE OF CUCURBITS. 
43 
develop mosaic symptoms after inoculation, and these healthy and 
diseased plants would remain intertwined for several weeks without 
further cases of mosaic appearing, no insects being present to cause 
infection. 
INSECT TRANSMISSION. 
I 
While dissemination of mosaic often occurs by the means already 
noted, a large part of the infection in the field is often due to insects 
attacking the cucumber. 
TRANSMISSION BY APHIS GOSSYPII. 
The importance of insects as a source of infection has been demon- 
strated by both Jagger (17) and Doolittle (11) in the case of the melon 
aphis (Aphis gossypii Glover), and field observations have repeatedly 
shown that this insect may be instrumental in the production of 
epidemics of cucumber mosaic. At Hamilton, Mich., in 1914, a 
I severe attack of aphids occurred over a wide territory during the 
latter part of July, when mosaic was present in a number of fields but 
had not become widely distributed throughout the district. As the 
aphids spread from field to field and increased in numbers, it was 
noted that a severe outbreak of the disease usually occurred about 
ten days after the appearance of the insects. Within a month most 
of the fields about Hamilton showed from 60 to 90 per cent of mosaic 
infection, and the crop was practically destroyed. Similar results of 
aphid infestation were noted in Michigan in 1916 and in Wisconsin 
in 1917, but over less extended areas. 
Table XVII.- 
- Transmission of cucumber mosaic by Aphis gossypii. 
Date. 
Treatment. 
Source of aphids. 
Number 
of aphids 
placed 
on each 
plant. 
Number 
of plants 
inocu- 
lated. 
Results. 
Number 
of mosaic 
plants. 
Date ob- 
served. 
Aug. 6,1915 
Aug. 23,1915 
Do 
Aug. 24,1915 
Do 
Aug. 30,1915 
Do 
Inoculated 
do 
Control 
Inoculated 
Control 
Inoculated 
. ..do 
Mosaic cucumber leaves 
do 
Healthy cucumber leaves . . 
Mosaic cucumber leaves 
Healthy cucumber leaves . . 
Mosaic cucumber leaves 
do 
25 to 30 
15 
30 
10 
20 
5 
3 
15 to 25 
10 
8 
6 
6 
3 
2 
8 
5 
3 
1 
10 
8 
8 
8 
9 
6 
7 
6 
10 
6 
9 
12 
8 
8 
8 
8 
6 
6 
6 
8 
8 
8 

9 

7 
6 

6 
9 
9 
7 
6 
2 

5 
1 


Aug. 21,1915 
Sept. 3,1915 
Do. 
Do. 
Do. 
Sept. 10,1915 
Do. 
Do 
Aug. 4, 1916 
Aug. 10,1916 
Aug. 5,1917 
Aug. 17,1917 
Do 
Control 
Inoculated 
do 
. .do 
Healthy cucumber leaves . . 
Mosaic cucumber leaves 
do 
Do. 
Aug. 14,1916 
Aug. 18,1916 
do 
Aug. 16,1917 
....do 
do 
Aug. 29,1917 
.do 
do 
Do. 
Do. 
do 
do 
Do. 
a Do 
((Sept. 1,1917 
Control 
Inoculated 
.do 
Healthy cucumber leaves. . 
Mosaic cucumber leaves — 
.do 
Do. 
Sept. 10,1917 
Do. 
Do 
do 
do 
Healthy cucumber leaves. . 
Do. 
Do 
Control 
Do. 
The agency of the insect in transmitting mosaic has been proved 
by experiments in which aphids taken from a mosaic cucumber plant 
were placed on healthy plants under cages. In nearly all cases, 
