14 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE, 194 4 
sodium fluosilicatc. barium fluosilicatc, potassium fluosilicate, and a 
low rotenone-containing product from t lie plant Dt-rri* lmihwcvnxi* 
(Benth.) Prain. The fluorine compounds bad a tendency to cause 
injury to cabbage, which limits their use as substitutes for the more 
desirable insecticides containing rotenone and pyrethrum. 
In combating the pea aphid in 1943, dusts containing nicotine sul- 
fate or rotenone combined with either nicotine or an organic thio- 
cyanate proved less elective than dusts containing rotenone as the 
only active agent. Against the tomato fruitworm basic copper ar- 
senate gave results superior to those obtained with calcium arsenate 
or cryolite, although DDT was the most effective insecticide tested 
against this important and widespread pest. In sprays for the Mexi- 
can bean beetle and the Colorado potato bettle good results were ob- 
tained with basic copper arsenate and micronized phenothiazine. Tests 
were made in Ohio to determine the relative efficiency against the 
Mexican bean beetle of two types of rotenone-containing dusts — 
ground derris or cube roots mixed with a diluent and impregnated 
dusts formed by depositing rotenone on the particles of the diluent. 
No differences in the results obtained could be detected, but since the 
dust mixtures are more easily prepared and less expensive than the 
impregnated materials, they would appear to be preferable for gen- 
eral use. 
The new soil insecticide dichloropropane-dichloropropylene (DD) 
has given promising results against wireworms in southern California 
and in Washington, and has also proved of value in preliminary tests 
against larvae of the green June beetle infesting tobacco plant beds. 
PROGRESS MADE IN ESTABLISHING RELATION BETWEEN INSECTICIDE DOSAGE 
AND INSECT CONTROL 
As an aid in the conservation of insecticides, si udies have been made 
on the most effective strengths and rates of application on several of 
the more important insects affecting vegetable crops. In field experi- 
ments directed against the pea aphid it was found that with dust 
mixtures containing from 0.25 to 1.5 percent of rotenone the quantity 
of rotenone applied per acre rather than the strength of the mixture 
governed the percentage of control. This relationship, however, did 
not prevail when the dust mixture was of lower rotenone content. For 
example, 60 pounds of a dust mixture containing 0/25 percent of 
rotenone gave approximately the same degree of control as '20 pounds 
of a dust containing 0.75 percent of rotenone; but 60 pounds of a 0.125 
percent rotenone mixture was not so effective as 20 pounds of a niixt ure 
containing 0.375 percent of rotenone. The results demonstrated thai 
when the recommended dosage of ; 33 pound of rotenone per acre 
was halved an appreciable reduction in control occurred. Moreover, 
a dosage one-fourth of thai recommended was sometimes effective 
under favorable conditions for control, hut the 0.33-pound dosage was 
required under un favorable conditions. 
M EC HANK A I . METHODS AID IN THE CONTROL OF INSECTS 
In in experimental area in Tennessee traps and poison feeders baited 
with amy] salicylate reduced hornworm infestations by approximately 
Mi percent. However, the same methods tested in the flue-cured 
tobacco growing districts of North and South Carolina were less 
effect ive. 
