EXPERIMENT STATION BULLETINS. 477 



when iucubated) the capacity for absorbing gasoline vapor remained 

 comparatively low. These facts surely seemed significant in connection 

 with the behavior of gasoline vapor, and the like, toward dormant in- 

 sects. 



It is a well known rnle that dormant insects are harder to kill with 

 fumigants (such as gasoline vapor, carbon disulphide, etc.), and that 

 they are more resistant to sprays of kerosene emulsion and the miscible 

 oils in general than are active insects of the same species. The question 

 naturally arose in this connection, therefore, as to whether insects in 

 the dormant state, from cold say, might not absorb less gasoline vapor 

 under a given fumigation charge than they would absorb when in the 

 active condition. In view of the close relation which the question bore 

 to the main problem of how contact insecticides kill, experiments were 

 planned to determine whether dormant insects would take up less of such 

 a fumigant as gasoline vapor than would be taken up by the same in- 

 sects after they had been brought into an active condition. 



Hibernating Luna moth pupae were selected as the first insects to be 

 used in these experiments, and gasoline vapor was the fumigant chosen. 

 This fumigant was used again in this case for the reason, already men- 

 tioned several times, that it permitted of accurate percentage determina- 

 tions of itself and of the oxygen and carbon dioxide present in the air 

 in which it was used. The pupae had been kept in the cold room of the 

 insectary all fall and winter until the experiments were first undertaken 

 December 17, 1913. The apparatus represented in -Figure III (except for 

 the hooked U-tube, and the burette "f") was moved into the cold 

 room six to eight hours before an experiment was to be begun, in order 

 that everything might reach the temperature of that room. Among the 

 accessories Avas a separate gas container with a stock supply of gasoline- 

 vapor-air, and a little water to maintain saturation with water vapor. 

 The dormant pupae were floated up on mercury in the gas container "c", 

 Fig. III. The mercury in the container was raised until almost all air 

 was exjjelled and the pupae were near the top. The outlet cock "t" 

 of the container "c" was then connected Avith the stock-container of 

 gasoline-vapor-air and the required amount of gasoline-vapor-air was 

 quickly drawn in with the pupae. Within the next half minute, a sample 

 of the gasoline-vapor-air with the pupae was drawn oft' above mercury 

 into a separate gas-container, to be kept for percentage estimations. The 

 mercury manometer, "m" Fig. Ill, was quickly leveled and the apparatus 

 was then watched until the first rapid loss in volume had passed, and the 

 manometer showed that no more gasoline vapor was being absorbed. 

 Then, a second sample of the gasoline-vapor-air confined with the insects 

 Avas drawn oft' for estimation in the same manner as the first. Both the 

 samples (one taken at the beginning and one at the end of the test) were 

 removed to the laboratory and alloAved to stand until they reached the 

 temperature of the room and of the apparatus (i. e. gas-pipettes and 

 compensation burette;- (see Fig. -1, p. 27, Tech. Bull. 11, this station) 

 used in making the percentage estimations. After that, the percentages 

 of gasoline vapor, of carbon dioxide, and of oxygen present at the be- 

 ginning and at the end of the absorption test with the pupae were de- 

 termined. From these results, kuoAviug the volume of gas present with 



*liy means of this burette, direct volume measuremeats at CC. nn<\ TGiQ m, m, mercury 

 pressure, with proper water vapor-tension corrections, could be made. 



