10 THE ALFALFA CATERPILLAR. 
It is the intention of the Bureau of Entomology to repeat these 
observations and experiments in the Southwest during the summer of 
1911, and in order to do so the bureau would be glad to cooperate 
with any farmers who wish to put their farms or ranches under a 
rigid system of control. The greater the number of farmers follow- 
ing this plan the greater the beneficial results that may be expected. 
METHODS OF CONTROL. 
INSECTICIDES, 
In dealing with insect pests affecting cereal and forage crops it 
has proved possible in only a few instances to control them by the 
use of any of the various insecticides or poisons. The reason for this 
lack of success lies largely in the fact that such crops are distributed 
over a wide area and the expense of application of any insecticide as 
a control measure is necessarily high, while a lack of thoroughness is 
likely to arise when one tries to keep the expense of treatment down 
to an economical basis. 
Since the alfalfa hay is fed to stock, it is not possible to use any 
of the arsenical poisons against the caterpillar of the alfalfa butter- 
fly. A few experiments were tried by using pyrethrum or “ buhach.” 
As this is not a poison, and since its fatal effect upon the larve of 
butterflies is produced externally through their breathing pores, 
there would thus be no danger to stock. Pyrethrum was used in one 
case at full strength, and in another instance it was diluted with equal 
proportions of flour. An application was made by dusting this sub- 
stance from a cheesecloth sack, following the primitive methed of 
applying Paris green to potato vines, at the rate of 3 pounds of 
pyrethrum to the half acre, which in the case of diluted material 
would make 14 pounds of pyrethrum to the half acre. This first 
test was tried on July 8, and no results were obtained, because of the 
fact that just two days later practically all of the worms in the field 
where the test was being made were destroyed by the malady before 
mentioned. The same experiment was repeated, however, on Septem- 
ber 22, and in this case also the results were negative, not a cater- 
pillar being killed. It would seem, therefore, that the application 
was not sufficiently heavy to kill the worms, and that to have 
increased the amount of pyrethrum applied might have resulted in 
the eradication of the pest; but as the cost of pyrethrum at the rate 
of 3 pounds to the acre is already nearly $2, without considering the 
expense of application by hand, this would be out of consideration 
from an economic point of view. However, the excellent results 
obtained through the use of pyrethrum in the case of other insects 
will justify further experimentation along this line, and it may be 
possible to use it in the smaller fields. 
[Cir. 133] 
