260 



bage worm, Pieris rapce. The old powder had settled together into a 

 sort of brick, and there seemed to be very little of the fine floating dust 

 in it, and when applied dry to the larvse would seldom kill one, but 

 when applied in water it did nearly as well, but not as well as the fresh 

 powder. This old pyrethrum was then ground very fine in a mill used 

 in the chemical laboratory for the purpose of grinding vegetable fibers,. 

 and then applied to other larvae and nearly every one that was well 

 dusted with this powder was destroyed, but it was not as powerful in its 

 action as the fresh powder. I give the results of the experiments ta 

 show that pyrethrum exposed to the air does not deteriorate so rapidly 

 as we would be led to suppose by the statements commonly made con- 

 cerning the extreme volatility of its essential oil. Although it is always 

 best to get a fresh article and keep it in a closed vessel, pyrethrum that 

 has been long on hand and much exposed is still valuable, and may be im- 

 proved by thoroughly regrinding. It was also found, by experiment, 

 that pyrethrum freshly mixed in cold water was as effectual in destroy- 

 ing the larvae of the cabbage worm as when allowed to stand overnight 

 or when prepared with boiling water. 



KEROSENE EXTRACT OF PYRETHRUM AS AN INSECTICIDE. 



In the summer of 1888, while experimenting with various substance* 

 for the destruction of the chinch bug, it occurred to me that a combina- 

 tion of kerosene and pyrethru m might form a most powerful insecticide 

 for external applications. The combinations were made by mixing the 

 dry pyrethrum into a previously prepared kerosene emulsion, by using 

 pyrethrum tea instead of pure water to dilute the emulsion, and by 

 extracting the powdered pyrethrum with kerosene and then emulsifying^ 

 this extract. I have used such an emulsion in comparison with an 

 ordinary kerosene emulsion for the destruction of the Chinch Bug, the 

 False Chinch Bug, Nysius angustatus, the Eed Spider, plant lice, and 

 cabbage worms, and it has been veryuniformly more successful than the 

 latter, but it will be necessary to experiment farther before drawing^ 

 definite conclusions as to the real value of the compound for the destruc- 

 tion of insects. I referred to my use of these substances in combina- 

 tion in Bulletin 5 of the Iowa Experiment Station, page 184. 



In discussing this paper, Mr. C, V. Riley called attention to the fact 

 that Mr. Albert Koebele should have the credit of first using success- 

 fully the resin compound in experiments which the former had planned 

 and directed. Mr. Riley also spoke of the varying results reached by 

 different experimenters in the use of kerosene emulsion, and said that 

 he thought these differences were largely due to the manner in which 

 the emulsion was prepared. He said : " In this connection I am 

 tempted to give a prominent illustration of this fact. No one has writ- 

 ten more of late years upon the subject than Mr. Cook, and yet from 

 his writings I had become convinced that he had never made a perfect 

 emulsion, as no one following his directions could, as the oil should be 



