14 BULLETIN 824, U. S. DEPARTMENT OF AGRICULTURE. 
periment stations in testing the efficacy of insect powder in destroying 
or repelling harmful insects, but a review of such work would be for- 
eign to the purpose of this bulletin. Those interested may consult 
the following list of references to recorded tests given in the bibli- 
ography (p. 83) : 2, 3, 9, 11, 26, 27, 28, 35, 36, 38, 44, 46, 49, 51, 52, 53, 
54, 55, 56, 61, 65, 66, 71, 72, 75, 87, 94, 96, 97, 98, 99, 100, 104, 120, 
125, 128, 129, 138, 141, 148, 149, 151, 157, 165, 167, 171, 176, 178, 
192, 193, 195, 200, 201, 203, 207, 208, 211, 217, 218, 221, 223, 
224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 241, 258, 262, 263, 
264, 270, 271, 272, 290, 291, 294. For a list of other articles on the use 
of insect powder against different insects, see "Bibliography of the 
More Important Contributions to American Economic Entomology, " 
published by the United States Department of Agriculture, Bureau 
of Entomology, Washington, 1890-1905. The "Index to the Liter- 
ature of American Economic Entomology," published by the Amer- 
ican Association of Economic Entomologists, 1917, gives references 
from 1905 to 1914. 
On looking over the literature it will be noted that the results of 
the various investigators of the powder differ in many respects. 
Some claim that the powder must be taken internally to be effective, 
while others state that it kills by external contact. In many cases 
the reported failures of the powder were no doubt due to the fact 
that a powder adulterated with powdered stems was used hi the tests, 
the experimenter accepting, as pure, commercial powders the compo- 
sition of which he had no way of knowing. 
At present insect powder is used largely against bedbugs, cock- 
roaches, ants, flies, mosquitoes, and certain other household insects, 
as well as plant lice, and fleas on pet animals. 
Although insect powder is an efficient insecticide against many 
insects, it appears that the plant from which it is made is not free 
from insect enemies. In 1884, W. Allan, of Baltimore County, Md., 
sent Riley (225, p. 416) specimens of Macrodactylus subspiuosus, found 
on Pyrethrum plants in large numbers and apparently eating both 
leaves and flowers, and Chauliognaihus marginatus, not so numerous 
and apparently attracted chiefly by the flowers. Riley states that 
a number of insects are known to feed on Pyrethrum while it is grow- 
ing. In 1890 Riley (229) again called attention to the fact that the 
Macrodactylus subspinosus, or rose chafer, devours the blossoms of 
the Pyrethrum cinerarisefolium. This fact, however, does not seem 
so surprising, as, according to Smith (263,264), insect powder is 
entirely ineffective against the rose chafer. 
EFFECT OF INSECT POWDER ON ANIMALS. 
While it is generally considered that insect powder is harmless to 
the higher animals, a number of cases where it has produced symptoms 
of a more or less serious nature are recorded. 
