. EXPERIMENTS AGAINST COCKROACHES. 9 



ACTION OF MATERIALS ON ROACHES. 



Upon careful study of the habits of roaches it has been found that 

 these insects frequently cleanse their legs and antennae. When any 

 dirt or powder comes in contact with the appendages, these are at 

 once drawn through the mouth parts of the insects and in this way 

 cleaned. As a result, a certain amount of any powdered substance 

 applied directly to a roach, or through which it may crawl, is thus 

 taken into the mouth. In this way any poison, whether distasteful 

 or not, finds its way into the stomach. Therefore it is not necessary 

 to mix a stomach poison, in powdered form, with an attractive bait, 

 since the chances are much greater that the poison will reach the 

 stomach of the roach through its habit of cleansing itself than 

 through the eating of the poisoned bait. 



True contact poisons, as, for example, mineral-oil sprays, kill 

 by coming in contact with the body. This may result (1) through 

 direct application or (2) by coming in contact with the roach after 

 it has been applied. 



Certain substances, such as sodium fluorid, will act both as contact 

 and as stomach poisons. 



Substances also may kill through gases given off, as in the fumi- 

 gation tests. 



KILLING EFFECT Ot POWDERED SUBSTANCES USED AS DUSTS AGAINST 



ROACHES. 



SODIUM FLUOEID. 



In Table II are given the results of tests with sodium fluorid in 

 kitchens and lunch rooms. 



Table II. — Results of tests with sodium fluorid against roaches in hadly in- 

 Jested kitchens, bakeries, lunchrooms, milk-bottle exchanges, etc. 



Test 

 No. 



Per cent 

 sodium 

 fluorid. 



other ingredients. 



Number 

 used. 



Duration 

 of test. 



Per cent 

 killed. 



1 



100 

 100 

 100 

 100 

 50 

 50 

 50 

 50 





Many 



...do 



48 hours... 

 ...do 



100 



2 





100 



3 





...do 



...do 



100 



4 





...do 



...do 



100 



5 



Wheat flour, 50 per cent 



...do 



-do ... . 



100 



6 



do 



...do 



5 days 



24 hours... 

 48 hours... 



98 



7 



Ground flint, 50 per cent 



...do 



100 



8 



do 



...do 



95 











As will be noted in Table II, sodium fluorid, when used undiluted 

 in badly infested kitchens and lunchrooms, kills practically every 

 roach within 48 hours, and there is almost no reduction of this 

 efficiency when it is used with equal parts of some inert substance, 

 as flour or ground flint. The substitution of ground flint for wheat 

 59108"— 18— Bull. 707 2 



