THE MOSAIC DISEASE OF CUCURBITS. 
45 
monly found on an equal number of plants in the same field. Checks 
were not run with the insects, as in field experiments it was impossible 
to determine with certainty whether or not the beetles had previously 
fed on mosaic vines. The results of these tests, shown in Table 
XVIII, indicate that the beetle must be an important agent of 
W transmission in most fields. 
Table XVIII.— Transmission of cucurbit mosaic by caging Diabrotica vittata over 
healthy cucumber plants, as shown by experiments made at Big Rapids, Mich., and 
Madison. Wis. 
Num- 
ber of 
bee- 
tles 
per 
cage. 
Source of the beetles. 
Method of infec- 
tion of beetles. 
Num- 
ber of 
plants 
per 
cage. 
Total 
num- 
ber of 
plants. 
Results. 
Location and date 
beetles were caged. 
Num- 
ber of 
mosaic 
plants. 
Date last 
observed. 
Big Rapids, Mich.: 
. July 28, 1916... 
'.n Aug. 4,1916.... 
Aug. 5,1916.... 
Aug. 11,1916... 
Aug. 14,1916... 
Madison, Wis.: 
Aug. 11,1917... 
Do 
8 
12 
8 
10 
8 
35 
32 
28 
30 
30 
30 
30. 
30 
20 
22 
27 
100 
40 
38 
45 
Madison, Wis 
Big Rapids , Mich . . . 
do 
Madison, Wis 
Big Rapids, Mich. .. 
Madison, Wis 
do 
Natural infection.. 
Fed on mosaic 
plants in cage. 
do 
Natural infection. . 
Fed on mosaic 
plants in cage. 
Natural infection. . 
do 
2 
2 
3 
3 
2 
8 
4 
7 
9 
7 
5 
5 
6 
6 
5 
6 
40 
18 
15 
15 
16 
2 
12 
12 
10 
8 
4 
7 
9 
7 
5 
5 
6 
6 
5 
6 
40 
18 
15 
20 
3 
1 
3 

4 
3 
1 
3 
5 
3 
1 
3 
2 
1 
2 
1 




Aug. 12,1916 
Aug. 17,1916 
Aug. 21,1916 
Sept, 5,1916 
Do. 
Aug. 21,1917 
Do. 
Do 
Do 
do 
....do 
do 
do 
Do. 
Do. 
Aug. 23,1917.. 
Do 
do 
do 
Sept. 4,1917 
Do. 
....do 
do 
Do 
do 
do 
do 
Do. 
Do 
do 
Do. 
Sept. 1. 1917... 
Do 
do... 
.. .do 
do 
do 
Sept. 12, 1917 
Do. 
Do 
....do 
do 
Do. 
Oct. 15,1917... 
do 
(Cucumber vines 
killed by frost.) 
do 
Oct. 30,1917 
Nov. 17,1917 
Nov. 21 1917 
Oct. 22,1917... 
do 
Oct. 27,1917 
do . 
do .. 
Nov. 10,1917.. 
.....do 
do 
Do. 
It will be noted that no beetles collected on or after October 15 7 
1917, produced infection. All cucumber plants were killed by frost 
about September 25, and all beetles collected in cucumber fields 
after that date had fed on other plants or on squash and cucumber 
fruits which still lay in the fields and had not fed on mosaic cucumber 
vines for three or more weeks prior to collection. In these tests 
plants were placed in a large cage in the greenhouse which held 40 
plants in small pots, and the beetles were allowed to feed on the young 
cucumber plants for several days. The results indicate that this 
insect can transmit the disease for only a short time after feeding on 
v mosaic plants. 
rJLABROTICA DUODECIMPTJNCTATA AS A CARRIER OF THE DISEASE. 
The 12-spotted cucumber beetle {Diabrotica duodecimpundata 
Oliv.) is also an agent of transmission of cucurbit mosaic in the 
field. This insect is so similar to the striped cucumber beetle that 
