HOW GASES ENTER INSECTS. 



William Moore, 



Division of Economic Zoology, Minnesota Experiment Station, 

 St. Paul, Minnesota. 



INTRODUCTION. 



Few experiments have been performed to show how insects 

 take in various gases, whether the gas enters through the 

 spiracles alone, through other openings in the chitin, or even 

 through the chitin. Schafer* has performed a few experiments 

 in which he placed insects in the gas hydrogen sulphide until 

 nearly dead, when they were removed and a warm solution of 

 lead acetate was injected into their bodies by means of a fine 

 hypodermic needle. A black precipitate of lead sulphide showed 

 where the gas had penetrated. In these experiments only larger 

 insects such as white grubs could be successfully used. 



Chitin as a rule is rather an impermeable substance and the 

 results in the larger insects showed that the gas had entered 

 through the spiracles. The question arises, Do the smaller 

 insects such as mealy bugs, white fly, soft scales, etc., which 

 have a much thinner layer of chitin depend alone upon their 

 spiracles for the penetration of gases into their bodies? After 

 trying several different agents, it was found that osmic acid 

 vapor could be used as a gas on the insects and would darken 

 the tissues where it entered the insect. 



METHOD. 



The insect to be studied was placed in a small vial in its 

 natural position on the leaf or stem and the vial suspended in a 

 large bottle containing crystals of osmic acid. The bottle was 

 then stoppered and placed under a bell-jar to prevent a leakage 

 of the gas into the room. The insects remained in the gas for 

 various periods of time, depending upon the insects, after which 

 they were removed, placed in alcohol, and through xylene, 

 finally being mounted in balsam for study. 



*Michigan Agricultural Experiment Station, Technical Bulletin, No. 11, 

 July, 1911, pp. 16. 



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