EMULSIONS. FOR JAPANESE BEETLE 9 



Table 6. — Comparative toxicity of four fractions of wormseed oil 1 l 



Fraction 



Properties at 25° C. 



Specific 

 gravity 



<|A) 



<!D) 



% 



D) 



Solution 

 in 70 per 



cent 

 alcohol 



Solution 

 in 60 



per cent 

 acetic 

 acid 



Percentage of larvae 

 killed by immersion in 

 dip for hours specified 



24 



First 



Second 



Third (ascaridole frac 



tion).. 



Fourth (residue) 



0.858 

 0.950 



1.0024 

 1. 0181 



—Strong. 

 -8. 73° 



-2. 41° 

 -2. 53° 



1. 4805 

 1. 4760 



1. 4720 

 1. 4780 



None 



6.5 vols 



1.4 vols 



0.5 vol 



Per cent 

 8 

 62.5 



100 

 97 



100 

 10O 



100 

 10O 



1 Temperature of dip in each case, 70° F. (21° C). The larvae were immersed for the specified number 

 of hours in the dip prepared from the fraction tested, and the percentage of those killed is tabulated. A 

 total of about 300 larvae were used in these tests. 



APPLICATION TO LARVAE IN SOIL AND PLANTS 



The results given in Table 4 indicate the action of wormseed-oil 

 emulsion dip upon the larvae when the latter are removed from their 

 habitat (the soil) and dipped. The larvae are killed in six hours at a 

 temperature of 70° F. When, however, the soil containing larvae or 

 infested plants (such as iris or phlox) is dipped in the material, it 

 must be submerged for a longer period in order to kill all the larvae 

 present. The soil itself apparently absorbs the toxic material from 

 the dip and interferes to some extent with the insecticidal action of 

 the material upon the larvae. This phenomenon of soil absorption 

 and its relations to the use of soil insecticides has been discussed at 

 considerable length in a previous paper by Leach and Thomson (3, 

 p. 58), and summarized as follows: 



Dipping tests indicate that certain compounds in solution, capable of produc- 

 ing a gas insoluble or only slightly soluble in water, are toxic to Popillia larvae. 

 These compounds may be divided into two classes: (1). Compounds slightly 

 soluble in water, e. g., carbon disulphide, thymol, mustard oil, etc. (2). com- 

 pounds readily soluble in water, such as sodium sulphocarbonate and sodium 

 ethyl xanthate. These compounds in solution, on being decomposed by organic 

 acids, yield carbon disulphide, the active killing agent. 



Saturated solutions of compounds in class 1 (about 1 to 1,000) readily kill 

 Popillia larvae when the latter are removed from the soil and dipped in the 

 solution for a definite period of time. However, when Popillia larvae are 

 embedded in a soil-ball and the latter dipped in these solutions the grubs con- 

 tained within the soil-ball remain unharmed. Soil adsorption, or, in other words, 

 physical "locking up" of the compound in solution by the moisture film surround- 

 ing the minute soil particles, is the apparent reason for the failure of these relatively 

 dilute solutions to function in soil. That portion of the compound adsorbed by 

 the soil is apparently rendered impotent as far as its ability to produce larval 

 mortality in the soil is concerned. 



Compounds of class 2, when used in dilute solutions give results comparable to 

 those obtained by the use of compounds in class 1. However, when compounds 

 of class 2 are employed in relatively concentrated solutions, a quantity of the 

 compound sufficient to produce 100 per cent mortality of Popillia larvae remains 

 free in the soil after the soil particles have adsorbed the compound to the limit 

 of their capacity. 



However, in the treatment of such plants as Japanese iris, phlox, 

 and sedum, the limitation above noted does not preclude success in 

 kilJing the larvae present in the root mass, for, while some soil is 



31469°— 25f 2 



