20 PROTECTION OF PLANTS, 1915-16 



II.— INSECTS IN RELATION TO TEMPERATURE 



It is a matter of considerable interest to know how the natural activi- 

 ties of insects are related to the temperature of the surrounding medium. 

 Recently Bachmetjew, by employing delicate thermo-electric apparatus 

 registering changes of temperature as small as .001°, has obtained results 

 of considerable value. 



His conclusions based on a long series of observations on insects are 

 as follows: — 



(a) The body temperature of insects at rest is practically the same as 

 that of the surrounding air. 



(b) Humidity is an important factor in modifying the efifects of tem- 

 perature.. In air of normal humidity the temperature of Deilephila is lower 

 than that of air when the temperature is raised. When paralysis of the wing 

 muscles begins the temperature approximates and at death is the same as 

 the air. If the air has a high humidity the moth has a higher temperature 

 than that of the air and with a rise in temperature this difference increases. 

 On the other hand,, when the humidity is lower than normal the tempera- 

 ture of the moth is lower than that of the air. 



(c) With the muscular activity due to body movements the temper- 

 ature rises and when movement ceases the temperature falls. The body 

 temperature of Sphinx pinastri rose 10°C. when it beat its wings rapidly, 

 but no rise was observed when its wings simply fluttered. 



(d) When an air temperature of 36°C. was reached the rapid wing 

 strokes ceased — the stage of "partial muscular paralysis." 



(e) With the gradual rise of the air temperature occurred a correspond- 

 ing rise of body temperature by rapid wing motion. For example, Deile- 

 phila raised its temperature from 19.2° to 34.8°, from 28.5° to 37°, and from 

 29°-34° to 42.1°. 



(f) Humidity has an influence on partial muscula^ paralysis — the drier 

 the air the earlier does paralysis set in. 



(g) The optimum air temperature is about 26°C. 



Above the optimum temperature are the regions of supra- optimum, 

 heat torpidity, transitory heat torpidity, permanent heat torpidity and 

 death. Permanent heat torpidity appears as a rule at 46°C., although 

 there are cases where it occurs several degrees lower, and also much higher, 

 as in ants and scale insects. Higher temperatures cause more rapid meta- 



