2 
BULLETIN 771, U. S. DEPARTMENT OF AGRICULTURE 
being recorded. With, each set of experiments checks, consisting of 
10 roaches dipped in fresh pyre thrum 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 I. — Effectiveness against roaches of whole and ground pyrethrum flower heads 
exposed to the weather or in a room. Ten roaches dipped for each test 
Material. 
Exposed— 
Number 
of weeks. 
Hours 
required to kill. 
No. 
First 
roach. 
Last 
roach. 
Average. 
1 
Whole flower heads : 
To weather 
do.. 
2 
12 
21 
2 
12 
21 
2 
12 
21 
34 
150 
2 
12 
21 
34 
136 
150 
150 
2 
12 
21 
34 
136 
150 
19.3 
19.6 
23.2 
19.5 
19.6 
23.4 
24. 
19.8 
14.5 
22.4 
18 
19.5 
19.7 
16.1 
22.1 
26.1 
42.1 
17.5 
19.3 
19.9 
23.5 
18.3 
22.3 
17.9 
43.3 
92.1 
31.2 
?, 
do . 
34.fi 
3 
do 
do 
3 active at end of 120 
4 
do 
hours. 
64. 5 1 as 
5 
do 
do 
47.6 
4 active a 
hoi 
64.8 
92.3 
71.9 
67 
44.5 
64.5 
43.9 
27.5 
46.5 
29.8 
f, 
do 
do 
t end of 120 
7 
Whole flower heads 
In room 
us. 
43.1 
8 
do 
do 
39 
q 
do 
do 
31 
in 
do 
do 
40.7 
11 
do 
do 
22 
1? 
Ground flower heads 
do 
39.5 
13 
do 
do 
do 
26 
14 
do 
22 
15 
do 
do 
36.4 
16 
do 
do 
t: end of 19,0 
17 
do 
do 
hours. 
8 active at end of 1 20 
18 
Whole flower heads 
In sealed jars 
do 
hoi 
41.5 
43.3 
44 
47.5 
46.9 
46.3 
44.1 
us. 
25.2 
19 
36.2 
?n 
do 
do ....... 
27.4 
?1 
do 
do 
30.7 
m, 
do 
do 
35.2 
?3 
do 
do 
28 
?4 
do 
do 
21.9 
1 Probably injured in dipping. 
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 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. 
