INSECT ECOLOGY 371 



that in dry air (evaporation 0.06 cc. per hour) running beetles of the 

 genus Pterostichus were very sensitive, exhibiting a preference for 

 moist air. Digger wasps, Microbembex, were slightly positive to dry 

 air, their chief reaction being digging, which took place in medium and 

 moist air but not in the dry. A tiger beetle, Cicindela, gave a nega- 

 tive reaction to air evaporating 3.6 cc. per hour, and a positive reaction 

 to air evaporating 1.56 cc. per hour. 



Shelford studied also the influence of rapidly flowing and of warm 

 air in increasing evaporation. All the animals that he studied could be 

 killed by loss of water, when other conditions remained favorable to 

 their existence. The smaller animals died from loss of water much 

 more quickly than the larger, the surface being greater in proportion to 

 the volume in the smaller animals. The animals died after a smaller 

 amount of evaporation when the rate was slow than when it was more 

 rapid. The most remarkable fact brought out was that the animals died 

 more quickly from evaporation due to rapid movement of air than due 

 to dryness. 



With a total evaporation of 31.0 cc. in a dry atmosphere Pterostichus 

 died in twenty- two hours. 



The Pterostichus referred to came from under leaves on the ground 

 in a dense forest a moist habitat; and Microbembex is a resident of 

 dry open sand areas. 



Hatching. With fertile eggs of plant lice (Aphis avence and A. 

 pomi) air of high moisture content is more favorable to hatching than 

 air having a lower moisture content. The moisture content of the air 

 influences the evaporation from the eggs, determines the percentage of 

 hatching, and probably influences the rate of splitting of the outer 

 layer of the egg shell. (A. Peterson.) 



Nymphs of walking-sticks, Phasmidae, frequently fail to extract 

 themselves from the egg shell, owing to dryness at the time of hatching. 

 Most of them succeed in escaping, however, if supplied with moisture. 

 In this instance evaporation has the mechanical effect of causing the 

 appendages or the abdomen to adhere to the amniotic membrane. (H. 

 P. and H. C. Severin.) 



Life Cycle. The length of the life cycle is often influenced greatly 

 by evaporation as determined by temperature and relative humidity. 

 With the Hessian fly, high temperature and low humidity lengthen the 

 cycle. In a dry atmosphere the eggs shrivel; in periods of drought 

 most of the puparia dry out and die. High temperature with high 

 humidity, however, does not retard the development, and is not fatal. 



