14 



BULLETIN 1332, U. S. DEPARTMENT OF AGRICULTURE 



with 20 cubic centimeters of carbon disulfide and adding N/10 

 KOH or N/10 NaOH until the solution is about neutral to phenol- 

 phthalein, 10 cubic centimeters of the hydroxide being ordinarily- 

 required. 



Theoretically, about 18.3 cubic centimeters of N/10 potassium or 

 sodium hydroxide is required to neutralize 0.5 cubic centimeter of 

 oleic acid, but in tests by mixing the acid with carbon disulfide it 

 was found that only 10 cubic centimeters of N/10 hydroxide was 

 required. This may be due to the solvent action of the carbon 

 disulfide upon the oleic acid, thus limiting the necessary neutralizing 

 action of the potassium hydroxide on the oleic acid at the surface of 

 the carbon disulphide globules, the acid in solution in the interior of 

 each individual globule probably not being acted upon. The neces- 

 sity for less than the theoretically correct amount would naturally 

 result from this condition. 



In the case of both of these carbon-disulfide emulsions water is 

 the external phase and carbon disulfide the internal phase, with a 

 hydrophile colloid as the emulsifier. 



Carbon-disulfide emulsion was tested along three lines: (1) Larvae 

 (not in soil) were submerged in the dip for various periods, to deter- 

 mine the time necessary at various temperatures for the dip to be 

 completely effective. (2) Peony roots infested with larvae were 

 dipped for various periods to determine the toxicity of the material 

 to the larvse under natural conditions and the resistance of the plant 

 to the insecticide. (3) The method was tested out under commercial 

 conditions involving the treatment of the entire croD of one of the 

 local nurseries. 



TOXICITY OF CARBON-DISULFIDE EMULSION TO LARVAE 



Larvse free from soil were dipped in dilutions of the carbon- 

 disulfide emulsion at different temperatures and for different 

 periods of treatment and the results noted. Two dips were used, one 

 of 4.2 cubic centimeters of emulsion 1, and the other of 4.57 cubic 

 centimeters of emulsion 2, each to 6 liters of water. The results for 

 the two were not separately recorded, the preference being slight. 

 The results in larvse killed for different temperatures and periods of 

 exposure are presented in Table 8. It is evident that the optimum 

 temperature lies between 60° and 70° F., the latter being preferable, 

 and that much of the effectiveness of the dip depends upon a tempera- 

 ture not too low. 



Table 8. — Toxicity of carbon-disulfide emulsion tc 



{not in soil) 1 



larvse of 



the Japanese 



beetle 



Temperature of dip (° F.) 



Percentage of larvse killed by immersion in dip for hours specified 



3 



4 



5 



6 



7 



8 



9 



12 



15 



18 



21 



24 



50 









25 

 100 

 100 

 100 



25 

 100 

 100 

 100 



50 

 100 

 100 

 100 



75 



100 



100 



100 



100 



100 



60 



75 

 100 

 50 



100 



75 

 100 



100 

 100 

 100 





65 















70 





























1 The larvse were immersed for the specified time, and the percentages of those killed are tabulated . A 

 total of about 400 larva? were used in these tests. 



