BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 53 
and for some unknown reason it appeared to increase the yield of 
cowpeas in the hull. Benzene hexaehloride, like DDT, did not injure 
rye following cotton as much as it did rye following cowpeas. The 
heaviest dosage of benzene hexaehloride imparted a reddish color to 
rye and oat plants, especially during the 19i8^L9 season. 
All insecticides were incorporated in the soil in order to test in as 
short a time as possible dosages comparable to residues that might 
eventually build up in practice. However, it is doubtful whether the 
accumulations that would result from normal applications of the in- 
secticides to foliage of held crops would be comparable to the high 
dosages tested. Most insect pests are controlled by foliage applica- 
tions of insecticides, some of which may be removed with run-off water 
or blown away by winds and therefore never become incorporated in 
the soil. 
It appears that the effects of DDT and benzene hexaehloride on the 
crops studied were dependent on a number of factors, including rain- 
fall and other seasonal conditions, the crop, the soil type, the insecti- 
cide, the dosage, the number of years the insecticide had been in the 
soil, and the crop rotation. 
New Insecticides Control Leaf Miners 
Progress was made in the development of methods of controlling 
several species of dipterous leaf miners, often referred to as serpentine 
leaf miners, which for the last several years have damaged tomatoes, 
sugar beets, peppers, lettuce, and cantaloups in California. Arizona, 
Texas, and Florida. Promising results have been obtained with para- 
thion. toxaphene, chlordane, dieldrin. and aldrin, although no entirely 
satisfactory control for the pests has been developed. DDT has not 
been very toxic to the leaf miners and in some tests reduced their insect 
parasites, resulting eventually in more leaf miners than when no 
insecticides had been used. Toxaphene dusts and sprays have gen- 
erally given good control on lettuce and sugar beets but cannot be 
used on cantaloups because of insecticide injury. Chlordane in dusts 
and in sweetened sprays has been effective in controlling the insect on 
cantaloups in Arizona. Parathion and dieldrin have given good 
control on cantaloups in Arizona and on tomatoes in California. In 
some of the experiments parathion has been the most effective insecti- 
cide, but it must be applied more often than the other materials. 
Chlordane, toxaphene, and dieldrin kill the larvae of the insect within 
the leaf tissues. 
Experiments are being continued to determine the best insecticides 
for the different crops and how they can be most effectively applied. 
For each crop greatest emphasis is being given to materials which, in 
addition to controlling the leaf miners, will be useful in controlling 
other insects that damage the crop. On cantaloups, for example, 
parathion has given promising results in controlling not only the leaf 
miners but also thrips, red spider mites, and the beet leafhopper, 
whereas dieldrin is not effective against the red spider mites. On 
tomatoes, dieldrin mixed with sulfur and talc shows promise for the 
control of leaf miners, the tomato fruitworm, and the tomato russet 
mite. The mixture cannot be used on cantaloups because sulfur 
sometimes injures this crop. 
