350 Report of the Department ok Entomology of the 



temperatures and in a dry atmosphere. Of the eleven successful 

 fumigations recorded in Table I — i.e., all larvae killed — seven were 

 in a moist air at a temperature above 67° F. and the other four at a 

 temperature of 70°. 



Table III. — Effect of Moisture on the Percentage of Caterpillars Killed. 



Data taken from Table T. 



THE RESISTANCE OF THESE INSECTS TO FUMIGATION 

 AND THE EFFECTS OF VARIATIONS OF TEMPERATURE 

 AND MOISTURE ON THIS CONDITION. 



The insects were in a state of hibernation, which is without doubt 

 the cause of this peculiar resistance to the poison. By hibernation 

 we understand that the insect is in a resting state and the water 

 content of the body is reduced. 11 In the caterpillar the openings 

 to the body are mouth, anus and spiracles. The spiracles are the 

 exterior openings to the trachese, ramifying tubes in the body, that are 

 filled with air and other gases. The air in the tracheal is separated 

 from the blood by the moist membrane of the tracheal wall. In 

 respiration the air passes through the spiracles into the trachea? from 

 whence the gases diffuse through the moisture in the membrane into 

 the fluids of the body cavity. The movement of the cyanide gas 

 into the organs of respiration is similar to that of oxygen. In a 

 dormant insect it enters the trachese largely by diffusion, while in an 

 active specimen, the gas is drawn in by the movements of the seg- 



11 Tower, W. L. An Investigation of Evolution in Chrysomelid Beetles of the 

 Genus Leplinotarsa. Carnegie Institution, Washington, D. C. No. 48, p. 245. 1906. 



