BULLETIN 198. 



THE GRAPE LEAF-HOPPER. 



of them would be killed by the heat. The optimum temperature under 

 these conditions was between 70 and 85F. The temperature of the 

 room during the experiments was between 65 and 75 F. In most of 

 the experiments it was the ordinary air of the room, as regards 

 humidity, but in some a moist plug of cotton was contained in the vial 

 with the insects, and thus the humidity was considerably increased. 

 The experiments in detail are tabulated below: 



Temperature Experiments. 



* Vial kept moist by wet plug cotton. 



fHeld for 10m. 



In the column "Inactive at" is indicated when the hoppers ceased 

 moving about, and in the column "Active at" when they first regained 

 their locomotive powers. The general conclusions suggested by these 

 experiments are as follows: 



A rise in temperature to 110F., and in one or two cases to 120F., 

 invariably killed the hoppers. With moisture in the tube they appeared 

 to withstand a slightly higher temperature. Cold to as low as 25F. 

 had no effect upon them except to make them temporarily dormant. 

 When they were subjected again to the higher temperature they were 

 killed the same as if started from the room temperature, except, 

 apparently, to make the first succumb at a lower temperature. The 

 practical bearing of these experiments can hardly be interpreted beyond 

 the fact that a sudden rise in temperature may be fatal to some of the 

 insects. In this the rather unnatural condition of dry, artificial heat 

 must also be taken into consideration. 



