82 BULLETIN 824^ U. S. DEPARTMENT OF AGRICULTURE. 



SUMMARY. 



The fact that flowers of certain species of Pyrethrum possess the 

 property of kilUng various insects was known to the people of eastern 

 Europe more than a century ago. Since that time this knowledge has 

 gradually spread, until insect powder is now a common household 

 convenience. This powder owes its insecticidal activity to a mixture 

 of acids and esters which first benumb and subsequently kill the in- 

 sects brought into contact with it. While it is generally considered 

 to be harmless to the higher animals, a number of cases where it has 

 produced symptoms of a more or less serious nature are recorded. 



At present insect flowers are cultivated commercially in Dalmatia, 

 Japan, Australia, Algeria, and California in the United States, the 

 first three countries producing nearly all of the flowers that enter into 

 international trade. The powder is made in each of these countries. 



In the enforcement of the Insecticide Act, insect powder has been 

 folind adulterated in a variety of ways. In some instances such sub- 

 stances as lead chromate, curcuma, and yellow ocher are added to give 

 color. Other species of flowers, like the Hungarian or oxeye daisy, 

 are substituted in whole or in part for the true insect flower, while 

 almond shells, brick dust, hellebore, pepper, sawdust, starch, sumac, 

 and the like have been found less frequently in samples examined. 

 The ground stems of the Pyrethrum plant, however, probably con- 

 stitute over 95 per cent of the adulterants used in insect powder at 

 this time. 



Physiological, chemical, and microscopical methods which can be 

 used satisfactorily in detecting adulteration with powdered stems 

 have not as yet been perfected to such a degree as to make an accurate 

 quantitative determination possible. However, from the data ob- 

 tained in the examination of hundreds of samples of genuine insect 

 powder, of the materials used for its sophistication, and of commercial 

 samples, the results of which are reported in this bulletin, a formula, 

 given on page 58, has been developed by which it is possible to deter- 

 mine in an insect powder the approximate amount of added Pyre- 

 thrum stems present. 



