EXPERIMENTS WITH HEAT AS AN INSECTICIDE 



There are numerous places where it is impractical to employ 

 gases, contact insecticides or arsenical poisons for the destruc- 

 tion of injurious pests, and in some of these situations heat may 

 be available. The work of Dean 1 indicates the possibilities 

 along this line in the case of several well-known mill pests. 

 It seemed advisable to test this with other insects, and the heat- 

 loving, oriental cockroach, Periplaneta orien talis Linn., 

 was selected as presumably a very resistant form. The work be- 

 gan with insects in vials, then in jars and finally in jars or paste- 

 board cylinders in a small room. In all instances observations 

 were possible throughout the test and the thermometers were 

 corrected by comparison with standard instruments. Great 

 care was exercised so to place the vials or jars containing the 

 insects that the walls could not become unduly heated with 

 consequent burning of the contained roaches. 



The apparatus employed in experiments I to 3 consisted of a 

 candy jar about eight inches high, in which was placed an 

 ordinary stab file supported on three wooden blocks so as to 

 separate its metal base from the glass bottom. A piece of soft 

 pine was fastened to the tip and from this a dairy thermometer 

 suspended so that it hung nearly in the middle of the jar and 

 touched no metal, its bulb being nearly an inch and a half from 

 the bottom of the jar and its top just below the cover. The 

 insects subjected to the test were suspended in the same way as 

 the thermometers. They were placed in two dram vials, the 

 free end being covered with coarse cheesecloth and the vials 

 hung so that they were nearly eight inches from the bottom of 

 the candy jar and free from contact with any metal. The candy 

 iar in turn was placed on wooden blocks in a shallow pan partly 

 filled with water, protected by an asbestos mat and placed on 

 a gas plate. 



Experiments 4 and 5 differed in that a quart fruit jar was 

 placed inside the candy jar described above. The insects were 

 provided with a slanting piece of cardboard for a support though 

 nothing was placed in the bottom. 



Experiments 6 to 8 differed from the preceding in that the 

 insects were better protected. Small blocks of wood were 



1 Dean, G. A. Econ- Ent. Jour., 1911, 4:142-58. 



[93] 



