The Potato Beetle in a Desert 



361 



the evaporation-rates, the transpiration curves, and the reaction graphs of these 

 organisms correspond ? The following experiments give us a further affirmative 

 response by showing that such a correspondence does exist in the potato-beetle 

 and other insects. 



The first experiment was performed out-of-doors at the foot of Tumamoc hill 

 near the experimental cages at Tucson Station A. The beetles which had 

 newly emerged from the pupa state were collected at night. They were kept 

 under saturated bell jars at a constant temperature until morning when they 

 were placed in wire netting tubes. At 11 a. m. on July 19 they were exposed 

 to the desert conditions in the open until 6 p. m. on July 31. The following 

 environmental conditions were determined hourly : the rate of evaporation, the 



5 6 



9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 2r 



Fig. 3. — Curves 2 and 3 show the relation of evaporation to transpiration 

 (water-loss) of beetles when exposed out-of-doors at the foot of Tumamoc hill ; 

 however, Curve 1 shows that the reactions of this insect to light were in general 

 the reciprocal of the evaporation and transpiration curves. 



air temperature, and the relative humidity. During this experiment, the entire 

 weight of the beetles was also determined, as well as periods when these insects 

 gave off water to the atmosphere. It is of importance to plant and animal 

 physiologists to state that these beetles absorbed water directly from the 

 atmosphere. Aside from these determinations, others were made, which 

 include the hourly loss in weight of these insects, the observed loss of water in 

 terms of their dry weight, the daily loss of water in terms of dry weight, and 

 the number of the beetles which were positive to light as well as the percentage 

 positive to light. These results are given in Table 7 and the figures in italics in 

 Table 7 show periods when the beetles absorbed water directly from the air. The 

 evaporation rates and the transpiration and reaction rates of Leptinotarsa are 

 plotted in figure 3. 



