220 SOME ASPECTS OF ECOLOGY 



larval or adult life, being greater at 15° than at 26° or 30° C, 

 but the factor of movement does not appear to have been taken 

 into account. 



Fatal Temperatures. A. Heat. A large amount of data has 

 accumulated in recent years with reference to the thermal death 

 point for many insects, but the results are discordant, and admit 

 of only approximate comparisons. This is largely due to the 

 fact that the length of time different insects were subjected to 

 different temperatures varied within wide limits, and the same 

 applies with regard to the interval elapsing between transference 

 from one temperature to another, the conditions of humidity and 

 other factors. In a state of nature the highest temperatures 

 under which insects regularly live are those prevailing in hot 

 springs and in deserts. In the case of hot springs (vide Brues, 

 1927), the highest temperature supporting insect life appears to 

 be 49° to 50°, Chironomid larvae being abundant at the first- 

 mentioned temperature in hot pools in the Yellowstone Park, 

 U.S.A. Coleoptera of the genera Hydroscapha and Bidessus are 

 regularly found in hot springs in Europe and North America at 

 temperatures varying from 30° to 46°. Buxton (1924) mentions 

 that certain insects are active in the Palestine desert on bare 

 earth whose surface temperature reaches 55° to 62°. The lethal 

 temperature for insects living in situations of this kind does not 

 appear to have been investigated, and the results would yield 

 data of considerable interest. 



With regard to other insects, it may be mentioned that Graham 

 found little difference in the thermal death points for the larvae 

 and adults of three species of beetles living in logs of timber, the 

 mean death point being between 46° and 48°, with a maximum 

 fatal temperature of 50° to 52°. In the case of the honey bee, 

 Pirsch (1923) found that the fatal temperature lay between 46° 

 and 48°. The grain weevils Calandra granaria and C. oryzw have 

 frequently been the subject of temperature experiments, and 

 Back and Cotton found that all stages were killed after one 

 hour's exposure to a temperature of 47-8° to 48-9°. Dendy and 

 Elkington (1920) found that three minutes' exposure to 48-9° was 

 the minimum time required to kill the adults of the first-mentioned 



