5:^ STATE nOARD OF ACRTCTTLTTTRE. 



pairing by some direct means the action of the muscles — especially 

 those that control the respiratory movements and the heart-action. It 

 might function as an agent whose presence would, in some manner, 

 interfere with metabolism or Avith tissue respiration in a part or all of 

 the body-tissues. 



The above outline is merely a list of general possibilities by no means 

 exhaustive in detail. It is given here in order to show the wide im- 

 port of the question, ''How Do Contact Insecticides Kill?" as well as 

 to suggest likelj^ lines for profitable investigation. Indeed, so few aro 

 the recorded experiments which are directed toward answering this 

 question that any of the possibilities suggested might be investigated 

 Avitli the hope of gaining useful evidence. A few experiments and facts 

 directly applicable have been lost sight of almost, and there has ap- 

 parently been no concentrated work on the subject. 



This experiment study has been carried forward, therefore, in the 

 hope of gathering useful direct evidence of some possibilities which 

 actually obtain and of bringing this evidence into such systematic re- 

 lation to the subject as to clear the way for further detail work along 

 promising lines. 



I. ON THIC EFFECTS OF CERTAIN GASES AND INSECTICIDES 

 UPON THE ACTIVITY AND RESPIRATION OF INSECTS. 



CAN CERTAIN CONTACT SPRAYS ENTER THE SPIRACLES AND PLUG THE 



TRACHEAE ? 



Wbile, in the past, little has been done directly on the subject, it 

 Ijas been the common belief, nevertheless, for a long time, that (out- 

 side of the very caustic sprays) contact insecticides kill by stopping the 

 breathing pores and thus suffocating insects. Numerous statements 

 to this effect may be found in entomological text-books and bulletins. 

 Since this idea is so commonly held, it was decided to determine first 

 of all if such insecticides as kerosene, miscible oils, etc., do enter the 

 spiracles and plug the tracheae of insects. 



Kerosene is so nearly transparent that its presence in the tracheae 

 of insects might be overlooked in a dissection, especially if present in 

 only small amounts. Sudan III, which is a stain soluble in kerosene, 

 giving it a strong red color, was therefore, used to make the fluid 

 easily visible wherever it should go in the insect. After a thorough 

 spraying with this colored kerosene, dissections of large insects like 

 Mclanoi^lus femoratus and the larvae of Phlegetliontius celeus showerl 

 more or less of the colored oil in the larger tracheae. In the case of 

 insects dipped in this colored oil for a few minutes practically all oi 

 the larger tracheae might be found filled Avith it. If a plant-louse witli 

 a delicate transparent body-wall was treated thoroughly with Sudan 

 III in oil and then the color was quickly removed from the outer sur 

 face of the body by means of unstained kerosene or gasoline, the red 

 oil could be seen through the transparent body-wall in some and often 



