INSECT POWDER. 



81 



From these results it is seen that the fruit from commercial sam- 

 ples of "open" flowei-s contains about 90 per cent of the total nitrogen. 



Practical tests were made by E. W. Scott and W. S. Abbott, of 

 the Bureau of Entomology, on roaches with the different parts of 

 the finely-powdered flowers, to determine their relative insecticidal 

 strength. The roaches were dipped in the powder until all parts 

 of the body were covered with it, and then placed in 8-ounce bottles, 

 one insect to a bottle, 10 insects being used in each test. All of the 

 insects were allowed ventilation, but no food or water 



The average 



of the 10 tests in each case is given in Table 49. 



Table 49. — -Insecticidal strength of JiJiehj-poivdered parts of insect flowers. 



Sample 

 No. 



Source. 



Entire "open" flowers of C. cinerarixfolium 



Fruit from sample 1 



Ray flowers from sample 1 



Receptacle from sample 1 



Involucre from sample 1 



Disc flowers from "closed" flowers of C. cineraria; folium . 

 Stems . 



Flowers of C. roseum. 

 Check 



Time 

 required 



to 

 paralyze. 



Minutes. 

 3.7 

 2.4 

 1,800 

 90 

 240 



Time 

 required 

 to kill. 



Hours. 

 21 

 19^ 

 63 

 50^ 

 80 

 31J 



131 

 23 



236J 



Apparently the fruit and disc flowers of the Clirysanthemum cine- 

 rarisefolium are the parts most active in paralyzing and killing roaches. 

 These are the same parts that show the highest content of nitrogen, 

 so that this element, although not actually a constituent of the active 

 principle, appears to be present with it in a constant ratio, and hence 

 can be used as a measure of the insecticidal activity. 



Summary of work on the active 'principle. — ^AU of the common organic 

 solvents completely remove the insecticidal principle from the flowers 

 of the C. cineranaefolium. The insecticidal principle is not re- 

 moved by a steam distillation, either in neutral, acid, or alkaline 

 solution. It is insoluble in water and dilute acids, but dilute potas- 

 sium hydroxid solution removes nearly all of the activity from the 

 powdered flowers. It is shown conclusively that the active principle 

 contains no nitrogen and is not an alkaloid. A considerable amount 

 of resin is present in Pyrethrum, but this is inert when tested upon 

 roaches. Alcoholic potash saponification completely destroys the in- 

 secticidal activity of the petroleum-ether extract, the ester being split 

 up into acids and resinous materials. The results of the work indi- 

 cate that the insecticidal activity of Pyrethrum is due to a mixture of 

 acids and esters. 



139815°— 20— Bull. 824 6 



