48 NINETEENTH REPORT STATE ENTOMOLOGIST OF MINNESOTA—I9Q22 
considerable depth of the powder and were thoroly coated with it. 
The powder was also mixed with flour and a little sugar and roaches 
were allowed to feed upon it. It proved an effective stomach poison, 
killing all the roaches experimented upon. 
It was found fairly effective under the average conditions in which 
such an insecticide would be used. The rat cages and the cracks in 
the rough board tables were fairly heavily infested with cockroaches 
(B. germanica) which fed upon the grain, etc., found in the litter of 
the cages and upon the tables about them. The usual harbor was 
beneath the cages. Derris powder No. 4 was scattered fairly thickly 
about the cages and dusted into the cracks of the rough pine tables. 
There was a very considerable reduction in the number of roaches 
and with continued treatment they practically disappeared for some 
weeks after the treatment was discontinued. 
In comparison with sodium fluoride for this purpose, derris has 
no advantage except that it is considerably less irritating to the mucous 
membrane of the nose, eyes, and respiratory passages; being, in fact, 
practically nonirritant unless inhaled in considerable quantities, when the 
tobacco dust will cause sneezing and coughing. 
It is believed that derris is not quite so efficient as fluoride, and 
undoubtedly is much slower in action, as well as more expensive. 
Compared with a goodly number of the patented roach powders, how- 
ever, it. is both much more efficient and much less expensive, besides 
having the added feature of being non-deteriorating, a glaring fault 
of most roach powders having pyrethrum as the insecticidal base. 
Derris should be ranked second to sodium floride as a roach exterminator. 
Some work was done with liquid derris. Its use upon animals 
is not to be recommended. The odor is very strong and repugnant to 
both animals and man, while the liquid is almost non-miscible and must 
be used with some sort of emulsifying agent such as soap, which 
makes it unhandy to prepare and use. As a spray for fruits and vege- 
tables it seems to have no properties to recommend it above the ordinary 
insecticides. Its efficiency is a little below the better nicotine prep- 
arations, while its cost is no less and its preparation is more difficult 
It does not mix well with sprays containing lime. It is, however, fairly 
effective and sticks well. Its effect if eaten with cabbage, lettuce, etc., 
is not known. It is very slightly toxic, altho probably not to a sufficient 
extent to cause illness in human beings in the quantities likely to be 
consumed. 
