152 Annals Entomological Society of America [Vol.111, 



Operation. 



In operating the incubator, it is necessary to set the automatic 

 apparatus for l)oth temperature and moisture. The former is 

 accomphshed by introducing a standard thermometer into 

 chamber E (fig. 3) and when the rising temperature reaches the 

 desired point, adjusting the electrode so that it almost touches 

 the rising mercury column in I) (fig. 2). The latter is accom- 

 pli.shed by introducing a standardized hygrograph into chamber 

 E. (Fig. 3) and when the rising relative humidity reaches the 

 desired point, setting the tension of the hair strand so that any 

 further loosening and lengthening will allow the platinum point 

 to make contact with the mercury. 



So long, then, as the heat maintains a constantly rising tem- 

 perature aild the ice in the tank is replenished, constant tempera- 

 ture will be maintained in chamber E (fig. 3) and so long as a con- 

 stantly rising relative humidity is maintained in chamber E 

 (fig. 3), and the calcium chloride is replenished, the constant rela- 

 tive humidity will he maintained. 



Its Use Illustrated.* 



Inasmuch as the data derived from use of the incubator in the 

 study of Toxoptera graminum Rondani are most available, they will 

 be used for illustration. 



The determination of the optimum temperature was first at- 

 tempted. The incubators were so j^laccd that they would get 

 the same quantity and quality of light. The moisture apparatus 

 was set at 75° relative humidity and the temperature a|)]iaratus 

 at difYcrent temperatures. A considerable number of indixidual 

 \i\'iparous Toxoptera graminum were allowed to complete their 

 life- cycles. The temperature was then changed and the experi- 

 ment repeated. This process was continued until the effect 

 of temperatures of 50° F., 70° F., 80° F., and 90° F.. under con- 

 stant relative humidity of 75° had been tested. 



It is generally accepted that the ojjtimum tem])crature of 

 an organism is that temperature under which the organism's vital 

 ])rocesses are most active. 



>■< The tem])erature under which these insects e.\])erienced the 

 lowest mortality and produced the largest number of healthy 

 young in a given time has been considered the optimum tempera- 



<• The writer desires hereby to acknowledge the aid afforded him by his student assistant, 

 Mr. Francis B. Millikcii, who under liis iinniediatc direction has tested ditVerent plans for the 

 control of moisture and collected data from tlie insects (\iider observation while the incubators 

 were in operation. 



