RELATIONS OF CLIMATE AND LIFE 103 



the body gradually adjusts and adapts itself for entrance into a dormant 

 state. We find adaptations against cold, heat and dryness, often in 

 cysts or in cases constructed by the creature, and in fact some of these 

 protective cases are made of substances impervious to water. In the 

 state of encystment far greater extremes can be experienced than in 

 the normal state, because of the impervious nature of the cyst. 



Successful dormancy often depends upon the rapidity with which 

 it was brought about. Most creatures practically free the intestinal 

 canal before entering a resting stage. 



A sudden lowering or raising of temperature may be fatal at tem- 

 peratures which would normally be easily withstood if approached grad- 

 ually. 



Alternation of high and low temperatures, if sudden, is often fatal 

 at normally effective temperatures. A creature may become dormant 

 with descending temperatures at a higher temperature than it would 

 awaken with ascending temperatures. 



A continuous maintenance of an even temperature and humidity is 

 more or less enervating. A climate which has sufficient variation to 

 allow certain periods of rest from cold at night and heat in the day 

 is probably productive of better results. It is possible in a given day 

 for a creature to have two active and two dormant periods. As for 

 example, observations of many insects will show that they sleep during 

 the cold parts of a night, are active during the morning, sleep during 

 the hottest part of the day, are again active in the evening and early 

 parts of the night. It is also noticeable that on humid days many in- 

 sects are inactive but as soon as the air dries they again resume activ- 

 ity, and the reverse is found in arid regions. 



Many investigators have failed in keeping insects alive for experi- 

 ment because of failure to keep sufficient water present for drinking 

 purposes and maintenance of proper humidity. 



As long as any creature is experiencing effective temperatures it 

 must have food available to take when needed and this food must be in 

 proper condition. Long periods without food at noneffective tempera- 

 tures can be experienced, but at effective temperatures the length of 

 life is relatively short. This is a very important point in control work 

 with all insects. If you can deprive them of food for a sufficient period 

 when the climatic conditions enforce activity, then control is easy. 



There are many very difficult points in this question. Inasmuch 

 as noneffective temperatures and also noneffective humidities may be 

 experienced each day, it becomes necessary to make elaborate studies 

 to ascertain the boundaries of the thermopractic and hygropractic zones, 

 and only a thermo-hygrograph record sheet will enable one to make any 

 kind of a satisfactory study. 



