BULLETIN 1332, U. S. DEPARTMENT OF AGRICULTURE 
year's growth. These cavities fill up with soil (fig. 2) and fre- 
quently afford shelter to larvae of the beetle. The larvae can be 
detected and removed only by cutting, which frequently ruins the 
plant. 
It has been found impossible to remove all the larvae from these 
plants by such ordinary expedients as shaking or washing. In 1920 
and 1921 only a portion of these crops was marketed, since no method 
was known whereby all the larvae present in the roots of the plants 
could be killed without injury to the plants themselves. Under 
these circumstances the writers undertook a study of this problem in 
an effort to discover a solution in which the plants could be dipped 
without injury to them for the purpose of killing any larvae present 
in their roots. 
PRELIMINARY WORK 
During 1920 and 1921 the writers con- 
ducted an extensive series of tests to de- 
termine the effect of various compounds 
upon the larvae of the Japanese beetle and 
upon the roots of plants. The experi- 
mental procedure in the case of each 
compound was the same ; larvae were dip- 
ped for varying periods of time in filtered 
solutions of the compound under investi- 
gation and the mortality of the larvae de- 
termined; potted plants, the soil of which 
was infested with larvae, were watered with 
the filtered solutions and the larval mor- 
tality and the effect of the compound upon 
the plant were observed. 
A partial list of the materials tested in 
this connection is given in Table 1 . They 
include inorganic salts, alkaloids, essen- 
tial oils, and representative compounds of 
the various organic groups. It will be ob- 
served that oil of wormseed not only con- 
trolled the larva but checked the plant 
only to a slight extent; carbon disulfide 
was somewhat more injurious to the plant. 
The other compounds were either innocu- 
ous to the larvae or killed the plants. In 
view of these results and in considera- 
tion of the great amount of experimental work required to test 
out each compound thoroughly the writers decided to limit the 
research to wormseed oil and carbon disulfide. 
IprL 
Fig. 1.— Japanese iris (Iris kaempferi) 
The matted root system with Japan 
ese beetle larvae interspersed 
