218 SOME ASPECTS OF ECOLOGY 



The influence of temperature upon insect metabolism can be 

 measured in the respiratory exchange by computing either the 

 carbon dioxide output or the oxygen consumption. The respira- 

 tory exchange is an extremely variable quantity, and the most 

 important influencing factor is functional activity. It is well 

 known that there is a certain minimum or basal metabolism 

 inseparable from the life of the individual. Basal metabolism 

 cannot be determined in the strict sense of the term, but an 

 approximation to it, corresponding to a minimum functional 

 activity, may be obtained, and is termed by Krogh (1916) standard 

 metabolism. The latter is regarded as the result of minimum 

 functional activity when voluntary muscular movements are in 

 abeyance, and no food is being taken or absorbed. In so far as 

 insects are concerned, the main source of error in many cases is 

 the difficulty of eliminating all muscular activity. Metabolism 

 due to the functional activity of the whole organism is an increased 

 metabolism over and above the standard. In many cases, in 

 dealing with adult insects or their larvge, standard conditions have 

 not been obtained, but such experiments require consideration 

 in the absence of the more exact data. Standard metabolism is 

 more nearly approached in the quiescent stages of the egg and 

 pupa, but the more rapid morphological changes undergone in 

 those stages are not characteristic of ordinary development. In 

 insects the respiratory exchange is high compared with other 

 animals, but, as Krogh remarks, since the experiments have been 

 made on a large number of insects at a time, the latter were often 

 probably restless, and consequently standard conditions wTre not 

 always obtained. 



The literature on the subject of respiratory exchange in insects 

 has been fully reviewed by Sayle (1928), but the available data 

 admit of few general conclusions. ^lost observers studying the 

 COg output in different stages of an insect record a reduction in 

 the, pupa as compared with the larva or imago. The amount 

 produced during a given stage generally rises with the temperature 

 within certain limits. Several observers, including Krogh (1914), 

 Weinland (1906) and Frew (1929), have shown that the respiratory 

 exchange (COg production) of insect pupae is high at first, then 



