54 ANNUAL REPORTS 01 DEPARTMENT 01 AGRICULTURE, L951 
Control of Onion Thripf Improved 
Experiments in cooperation with the [daho Agricultural Experi- 
ment Station showed that dust mixtures or sprays containing DDT. 
toxaphene, parathion, and chlordane were about equally effective and 
gave excellent control of the onion thrips on commercially grown 
t » 1 1 1 1 » onion- in Idaho. The new insecticides, now used extensively 
h\ growers, are a marked improvement over the nicotine-sulfate and 
tartar emetic sprays formerly used. Preliminary tests in Idaho dis- 
closed that a newly introduced insecticide -an ethyl p-nitrophenyl 
thionobenzene phosphate— has potential value for the control of the 
onion thrips when used in a spray. In experiments in California dust 
mixtures containing chlordane aldrin, parathion, toxaphene, and 
lindane were equal to or slightly superior to DDT dusts in the control 
of the onion thrips and gave increased yield- of hnlh onion- in com- 
parison with DI >T dust. 
iphids Transmit \ iras of Dahlia Mosaic 
At least five species of aphid- transmit the virus of dahlia mosaic 
that causes the decline of many commercial varieties of dahlia-, ac- 
cording to results of experiments at Beltsville, Md.. in cooperation 
with the Bureau of I Man t Indn-t ry, Soils, and Agricultural Eng 
iiiL r . The green peach aphid and the potato aphid were found to be 
the species most capable of transmitting the virus. The bean aphid. 
melon aphid, and foxglove aphid were slightly less capable. The 
aphid- transmitted the virus in a nonpersistent manner; that is, they 
he. •nine infectious by feeding for a minute on a diseased plant, after 
which they were able to infect a high percent ant' of the healthy plants 
they [\'(\ on during the next 2 hour-. By the end of that period they 
had lost their ability to transmit the virus. Aphid- starved before 
feeding on diseased plant- were more efficacious as vectors of the dahlia 
mosaic virus than aphid- i\^\ normally. Dahlia mosaic was trans- 
mitted by virus-carrying aphid- to zinnia and to three ornamental 
species ol plant- closely related to dahlia. Dahlia mosaic symptoms 
developed more quickly in zinnia than in dahlia or its related -p> 
Zineb Fungicide lias Incidental Lnsecticidal Effecl on Pickleworm 
iiiid Melonworm 
Experiments on the control of the pickleworm and melonworm in 
South Carolina showed that the fungicide zineb is toxic to these insects 
when it is applied primarily for the control of plant diseases on i-u- 
cumbers. 
( Cucumbers in commercial fields and experimental plots where /.inch 
was applied were less heavily infested with the pickleworm and melon- 
worm than those in plot- where no insecticide was used or where 
fungicides other than /inch were applied. Application of /inch to 
cucumbers in dusts or sprays, at the dosages ordinarily \\^i^\ to com- 
bat plant diseases, killed approximately 50 percent of thepartly grown 
pickleworms in laboratory and small scale field tests. The fungicide 
< 1 1 < I not kill the full grown pickleworms and was only partially effec- 
tive in protecting the cucumber fruits from infestation. 
