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. 



Fig. 1. — Japanese iris (Iris kaempferi): 

 The matted root system with Japan- 

 ese beetle larvae interspersed 



