The Potato Beetle in a Desert 



363 



at night by aid of a light, and were collected as soon as possible after emergence. 

 All were placed at once in bell-jars in the constant-temperature room. A high 

 relative humidity was produced as before by placing a wet filter-paper inside 

 the jars, which permitted the animals, if not already saturated, to absorb water, 

 so that their water-contents would be as uniform as possible, and they would 

 attain, in this respect, a similar physiological equilibrium. The insects were 

 retained under these conditions until 10 a. m. the following morning, when they 

 were exposed in similar cylindrical tubes. The instruments for measuring 

 environmental conditions were also placed in these tubes, which were suspended 

 to a wire and placed in the open, so that each tube was inclined toward the north. 

 The direct rays of the sun were thus permitted to fall upon the tubes at right 

 angles. Unless otherwise indicated in Table 8, the observations were made 

 hourly from 11 a. m. July 19 to 6 p. m. July 21, and for the environmental 

 conditions consult Table 7. 



3.0% 



2.5% 



S'2.( 



S 1.5% 



1.0% 



35° 



S 

 H 30° 



25° 



20° 



Hourly 

 Units 12 3 4 5 6 7 



3.0?, 



2.5%' 



1.5% a; 



70% 



60°^^ 

 £ 



50t > 



40% < 



30% 



9 10 11 12 13 14 15 16 17 18 19 20 21 22 

 Fig. 4. 



24 25 26 



28 29 



If one should plot the results given in Table 8, he will find that all of the 

 organisms used give a transpiration curve which corresponds with their curves 

 of evaporation. Catalpa lanigera and the crickets reacted to transpiration in a 

 manner not unlike the potato beetles, while the Lachnosternae always gave a 

 negative response, regardless of conditions. 



Another experiment upon loss of water and insect activity was made as a 

 conformatory test, in which the methods and materials used were similar. The 

 animals consisted of 31 L. decemlineata (Tucson A, g. Ill), 10 Catalpa lani- 

 gera, and 20 Laclinosternse. The latter were collected around an electric light 

 and then placed in a refrigerator. All instruments and insects were exposed 

 in the open in large netting spheres and hourly observations were made from 

 9 p. m. August 9 to 4 p. m. August 11 ; the complete data are given in Table 9. 

 The evaporation-rates, the air-temperatures, and the relative humidities are 



