2 BULLETIN 771, U. S. DEPARTMENT OF AGRICULTURE 
being recorded. With each set of experiments checks, consisting of 
10 roaches dipped in fresh pyrethrum powder and 10 untreated, were 
used. The average mortality for the untreated roaches was found 
to be less than one roach in 108 hours, which is so small that the 
untreated series were omitted from the following tables. 
EFFECT OF EXPOSURE TO WEATHER AND IN A ROOM 
Table I shows the killing effect on roaches of whole and ground 
flower heads that had been exposed to the weather or in a room for 
various periods of time. 
TaBLE |.—Effectiveness against roaches of whole and ground pyrethrum flower heads 
exposed to the weather or in aroom. Ten roaches dipped for each test 
Hours required to kill. 
oy Number 
pele Matcral: ; i dase Seas: | Tafasti Last |, 
roach. | roach. verage. 
2 19.3 43.3 31.2 
12 19.6 92.1 34.6 
21 23.2 dectives atend of 120 
urs. 
2 19.5 64.5 35 
12 19.6 47.6 29.8 
21 23.4.) 4active at end of 120 
hours. 
2 24 64.8 43.1 
12 19.8 92.3 39 
21 14.5 71.9 31 
34 22.4 67 40.7 
150 18 44.5 22 
19.5 64.5 39.5 
12 19.7 43.9 26 
21 16.1 27.5 22 
34 22.1 46.5 36. 4 
136 26.1 | lactive at end of 120 
| hours. 
150 42.1 | 8active at end of 120 
hours. 
150 17.5 41.5 25. 2 
19.3 43.3 36.2 
12 19.9 44 27.4 
21 23.5 47.5 30.7 
34 18.3 46.9 35. 2 
136 22.3 46.3 28 
150 17.9 44.1 21.9 
1 Probably injured in dipping. D 
The material used in these experiments was received as whole 
flower heads in April, 1915, when it was divided into six lots which 
were treated as follows: 
No. 1. Whole flower heads, in a large open glass cylinder, were 
placed out of doors where they were fully exposed to the s sun, wind, 
and rain. : ; 
No. 2. Powdered flower heads, sifted to 80 mesh, were exposed 
as in lot No. 1. 
No. 3. Whole flower heads were placed in a shallow dish and al- 
lowed to stand on a shelf in the laboratory. 
_ No. 4. Powdered flower heads (80 mesh) were exposed as in lot 
No. 3. 
