484 STATE BOARD OF AGRICULTURE. 



In order to be able to see just where the powrler went, when it came 

 in contact with the body of an insect wearing: a collar, both borax and 

 sodium fluoride were stained with either sodium carmine, or indigo 

 carmine, after which they were thoroughly dried and pulverized to a 

 powder. In a few cases, where dissections were to be made under water, 

 Sudan III was used as the" stain for the insecticide powder. Individual 

 experiments were cnrried out willi more than forty insects according 

 to the outline just given, and all these were in agreement as to the ques- 

 tion considered. It was found that powdered borax and powdered sodium 

 fluoride could bring about the death of roaches through being dusted 

 flioroughly on their bodies, without ever having come in contact with 

 the mouth. The dusting of the body was done through the efforts of 

 tlie insect itself, in scrambling and fluttering with the legs and wings 

 in the manner already explained. Borax required two to ten days to 

 cause death through contact of the powder alone. Sodium fluoride re- 

 quired from five to twenty-two hours. In each case the average time 

 was much longer than was required to bring about death when the insect 

 had eaten some of the powder in cleaning the same from its body. The 

 symptoms folloAviug contact alone were usually very similar to those 

 which followed when the poison had been eaten. As a rule, the period 

 of partial paralysis and helplessness was much more prolonged when 

 the powder had been used only as a contact insecticide. The exudation 

 which caused the powder to stick to the roach's body was nearly always 

 sufficient to dissolve enough of the borax or sodium fluoride to cause 

 incrustation at the bases of the legs, between the sternal plates, etc. 



In seventeen of the experiments in which the stained insecticide powder 

 (sodium carmine was the stain mostly used) had been employed, the 

 insects were dropped into a hot alcoholic fixing fluid at about the time 

 of death. Afterward, parts of the bodies of these insects were embedded, 

 and sectioned. A study was made of the miscroscopic sections prepared 

 in this way. in order to learn bv means of tlie stain if nossiWe, whether 

 the powder had entered the spiracles — or had passed, after solution, 

 into the insect's body through the thinner ])ortions of the body wall. 

 The sections showed the incrustations of the stain at the bases of the 

 legs, between the sternal plates, and (sometimes) just within the spir- 

 acles in the vestibule from which the tracheae arise; but no stain was 

 found further within the trachea?, and no sections w^ere found which 

 showed undoubted evidence that the stain had penetrated the integument 

 to stain the hypodermal cells. If the cuticula was permeable to the 

 stain and to the borax or sodium fluoride solutions in the same degree, 

 then it is certain that only a very limited amount of the insecticide 

 passed into the animal's body through the thinner portions of the body 

 integument. The latter, however, seems to have been the po.ssible and 

 probable path. No indication was found that the stained insecticide 

 powder had entered the bodies of cockroaches Aveariiig the collars, in 

 any other way. It must be remembered that the sodium fluoride rendered 

 roaches helpless and practically dead in some cases within five hours — 

 i. e.. during the time the insects were wearing the collars, and sections 

 showed no trace of stain in the crops of these insects. It took the borax 

 so long to kill by contact that in the first tests, the roaches were brushed 

 as clean as possible after six to eight hours treatment, and were then re- 



