306 
. Journal of Agricultural Research 
Vol. XXVIII, No. 4 
Table V.— Inoculation of sugar beets with insects other than Eutettix tenella, no 
disease resulting 
Season, number, 
and date 
Season of 1915: 
No. 1, Aug. 30— 
No. 2, Aug. 30... 
No. 3, Aug. 30- 
No. 4, Aug. 30... 
No. 5, Aug. 30- 
No. 6, (?). 
No. 7, (?)- 
Season of 1917: 
No. 8, Aug. 29- 
No. 9, Aug. 29... 
No. 10, Sept. 4— 
No. 11, Sept. 4— 
No. 12, Sept. 4., 
Season of 1917: 
No. 13, Sept. 14.. 
No. 14, Sept. 14.. 
No. 15, Sept. 4.. 
Season of 1919: 
No. 16, May 22- 
No. 17, May 22- 
No. 18, May 22- 
No. 19, May 22— 
No. 20, May 22- 
No. 21, July 1.. 
No. 22, (?). 
No. 23, Apr. 28.. 
Season of 1920: 
No. 24, Feb. 23- 
Species of insect 
Empoasca viridescens.— 
Agallia spp__.. 
Thamnotettix gemina- 
tus (?). 
Cicadula 6-notata. 
Liburna sp_. 
Empoasca viridescens... 
Agallia spp._. 
Empoasca viridescens... 
Agallia cinerea. 
Empoasca viridescens.._ 
Nysiussp.... 
White fly (Aleyrodidae). 
Aphissp. 
_do__. 
Lygus pratensis_ 
Acinopterus sp.. 
Chlorotettix sp. 
Agallia sp. Qarge)_ 
Agallia cineiea. 
Empoasca viridescens... 
Thamnotettix montanus 
Aphis sp... 
Eutettix strobi.. 
Empoasca viridescens..^ 
Num¬ 
ber of 
insects 
used 
7 
7 
6 
6 
12 
Large. 
Large. 
10 
Large. 
3 
6 
Length of time 
insects were on 
curly-top beets 
Healthy plant 
to which the 
insects were 
transferred 
4 days_ _ 
Young beet_ 
_do__. 
.do.. 
__ _dn 
.do_ 
.do-. 
.do__. 
.do_ 
Collected from dis¬ 
eased plants. 
Collected from dis¬ 
eased plants in 
the field. 
47 days_ 
.do.. 
_do. 
.do.. 
(a). 
35 days — _ 
(a)_ 
39 days _ _ — 
(a)__ . 
29 days_ 
(a) _ 
.do.— 
(ay .: . 
(2) (6) . 
(3) (c)_ 
29 days _ 
(a). 
4 days.. 
Young beet. 
.do... 
_do.. 
13 days . _ 
.do.. 
_do--.. 
_do___ 
20 days. 
4 days.. 
.do—. 
.do... 
3 days _ 
(d). 
2 days... 
Young beets_ 
Several days. 
Young beets and 
Stellaria media. 
Length 
of time 
insects 
were left 
on 
healthy 
plants 
28 days. 
Do. 
Do. 
Do. 
Do. 
22 days, 
Do. 
47 days. 
35 days. 
39 days. 
29 days. 
Do. 
29 days. 
15 days. 
Do. 
Do. 
44 days. 
37 days. 
27 days. 
2 days. 
18 days. 
° The insects were placed in a cage with a small curly-top beet and a small healthy beet for the number of 
days stated. 
& A curly-top beet leaf heavily infested with aphids was placed in a cage with healthy and curly-top 
plants. The insects colonized on both plants. 
c A curly-top beet leaf heavily infested with aphids was placed in a cage with a healthy plant upon which 
the insects colonized. 
d A curly-top leaf with aphids on it was removed to a cage with a healthy beet and another to a cage with 
two healthy Stellaria media plants. 
Observational evidence agrees with these negative results from attempts to 
transmit the disease by insects in so far as aphids and Empoasca viridescens are 
concerned. These two species have been repeatedly observed infesting the 
plants in cages which contained both curly-top and healthy plants and in no case 
has there been any evidence that they transmitted the virus of the disease. 
The question of transmission by grafting perhaps should be considered in this 
connection. Smith and Boncquet {15) claim to have transmitted the disease 
by grafting parts of diseased beets on to healthy plants. Thus far the present 
writers have been unable to successfully graft parts of a curly-top plant on to a 
healthy plant, and the attempts to make these grafts have not produced the 
disease. 
<► 
IS THERE AN INCUBATION PERIOD IN THE LEAFHOPPER? 
As has previously been stated, Eutettix tenella is the only known agent or means 
by which the virus of curly-top can be transmitted. Also, the fact has been 
pointed out that the ability to produce the disease is not an inherent characteristic 
