576 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 17 
and apparently living under favorable conditions as regards humidity 
and temperature. To supply a possible explanation for the same a 
rather long line of tests was conducted by supplying food materials in 
varying amounts to open mouth bottles and introducing into this food a 
definite number of beetles; a careful count to be made of the mortality 
rate at different intervals of time. As a result of these tests it was 
shown: that apparently the greater the air space, the more pronounced 
the increase in the rate of mortality. As a check upon these tests two 
other experiments were determined upon: one by supplying mechanical 
means for making it possible for the beetles to maintain a position near 
the opening of the mouth of ■ a bottle containing little food and the 
other, by means of an air suction pump to supply a constant change of 
atmosphere to a bottle containing a small amount of food. These and 
the other tests mentioned indicated that some factor or factors entered to 
bring about a lethal effect upon the adults of these beetles, and these were 
more or less dependent upon the amount of atmospheric space above the 
meal and below the opening of the mouth of the bottle, unless a con¬ 
stant change of atmosphere was supplied in which case the rate of 
mortality was lowered. 
A number of factors to account for the above might be suggested,—- 
carbon dioxide, a gas heavier than atmosphere and a gas given off during 
respiration of the beetles or grain, a diminished oxygen supply, a gas or 
gases as yet unidentified, are within the limits of possible causes. 
Following the suggestion that C0 2 may be the toxic substance and 
possibly its source, the product of the meal in which the beetles were 
kept, this meal was heated to 115°C. for one hour to make ineffective 
the enzymes for C0 2 production, it was found however, that the rate of 
mortality of beetles living in that material was higher than that of 
beetles living in unheated material, so if C0 2 is the toxic substance it 
must come as a product of the metabolism of the beetles. 
Effect of Humidity on the Rate of Development of Echocerus 
cornutus. Headlee, Parker and others have shown that humidity has 
an effect upon the rate of metabolism of insects. In order to determine 
in a general way, the effect of varying degrees of humidity on Echocerus 
cornutus I designed the following experiment. One hundred and twenty- 
five adult beetles, and one hundred larvae in last instars, were placed in 
open cartons containing germea and then placed under bell jars under 
varied moisture conditions, the humidity of the bell jars being con¬ 
trolled by drawing air thru a calcium chloride dryer, which gave it a 
humidity of less than 1% and then passing this thru concentrated solu- 
