49 



soil, but are weak and almost inactive; have a dirty-yellow color and 

 occasional black spots. Saw no dead ones. Around margins of plat 

 treated and in other places found the larva? abundant and doing injury. 



The lawn was not visited again until July 27. At this time I could 

 not tind Mr. Cogan, so no complete examination was made. No grubs 

 could be found in the surface soil of the plat treated ; elsewhere they 

 were abundant, but no steps had been taken to check them. 



July 31, went to the Capitol and Mr. Cogan and myself, with the as- 

 sistance of a laborer, made a full examination of the plat treated. No 

 grubs were found in the surface soil, but on spading down 8 to 12 inches 

 some were found; further search showed them at a depth of 16 inches. 

 Careful examination of about 3 square feet of surface to a de[.th of 16 

 inches brought to light fourteen grubs, all dead and discolored, as before 

 mentioned. Not a living larva was found by examination on the treated 

 plat. A spot nine paces to one side of the treated plat was examined 

 and here grubs were found about as numerous as before, a few of which 

 were dead and showed the same discoloration before mentioned. We 

 then examined a spot 150 feet from the treated plat and found the grubs 

 very numerous, some thirty being counted on 3 square feet examined. 

 These were in no wise afiected, tending to prove that those found in 

 second place examined had crawled away from the treated plat. 



This is one of the most satisfactory experiments I have ever made 

 with kerosene emulsion. Mr. Cogan stated that he used a small i^ortion 

 of the emulsion diluted but eight times, and found that it did not injure 

 the grass. However, there is no object in using it so strong, as it is 

 easily applied, and we believe the very abundance of water helps to 

 carry the kerosene into the soil. This was the purpose in having the 

 ground treated so freely watered. Compared to our previous experi- 

 ments for the destruction of white grubs (Bull. 13, Division Ent., 1887, 

 p. 39) the results are similar up to a certain point, but where the earlier 

 experiments ultimately resulted in failure we think the reason is to be 

 found in the lack of facilities for drenching the soil. It would require 

 a large quantity of the diluted emulsion to penetrate the soil to any 

 depth. The emulsion was prepared according to the original formula 

 published by this Division, and frequently repeated in Dr. Riley's offi- 

 cial reports. 



The following communication from Mr. Cogan may be taken as a 

 thoroughly fair opinion of the success of the above experiments: 



United States Capitol Grounds, 



Washington, D. C, August 2, 1888. 

 Sir: Early in the month of June I submitted to your Department specimens of 

 grubs which I found destroying the grass on the lawns of the United States Cap- 

 itol grounds. 



Your assistant, Mr. Alwood, immediately investigated, and under his instructions 



the places affected were thoroughly drenched with an emulsion of kerosene in the 



proportion of one to sixteen, and the ground then well watered. I found that where 



this emulsion was used the grubs immediately ceased their depredations, penetrated 



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