

THE METABOLISM OF INSECTS 



By MARY HONORA SAYLE 



Zoology Laboratory, University of Wisconsin 



INTRODUCTION 



INSECTS, because of their abundance 

 and wide variety in form and struc- 

 ture, have proved to be interesting 

 animals for observation and study. 

 From the naturalist, we have learned much 

 about their habits. The entomologist 

 has classified this large group of animals 

 and has contributed to our knowledge of 

 insect anatomy and physiology. In the 

 more recent years insects have been used 

 in desiccation studies, and a great deal 

 has been written about their ability to 

 withstand drying. The question of the 

 effects produced on them by high tempera- 

 tures is one which has received the atten- 

 tion of biologists for many years. The 

 older workers were interested chiefly in 

 the determination of the so-called "upper 

 thermal death points." A resume of 

 their observations is given by Davenport 

 (8). Spallanzani (19) as early as 1787 

 wrote about the tolerance of insects to 

 high temperatures. He determined the 

 death points of flies, silkworm and butter- 

 fly larvae, and the larvae of the mosquito. 

 These forms ranged in their high tempera- 

 ture tolerance from 37. 5 to 43-5°C. 

 Plateau (2.2.) determined experimentally 

 the thermal death point of a number of 

 fresh water insects known to occur in 

 thermal waters as well as in ordinary 

 ponds and streams. The unacclimatized 

 animals were kept in water, the tem- 

 perature of which was gradually raised. 

 Roedel (2.4) determined the ultra-minimum 

 temperature of such forms as the honey 



bee and house fly. The house fly can 

 resist — iz°C. for five minutes and — 5 

 for 40 minutes. The work done on tem- 

 perature tolerance and acclimatization is 

 interesting. A review of this subject with 

 reference to high temperature is given by 

 Brues (6). 



HISTORICAL 



More recently a number of biologists and 

 physiologists have been interested in the 

 metabolism of insects. Are insects affected 

 by changes in temperature, light, and 

 food supply? Investigators have found 

 that their life processes are markedly 

 affected by environmental changes. The 

 metabolic processes taking place inside 

 the body of an animal can be measured in 

 the respiratory exchange of the animal by 

 ascertaining either the oxygen consump- 

 tion or the carbon dioxide output. From 

 the results of various investigators it is of 

 interest to note that the respiratory rates 

 for insects are considerably higher than 

 those of other animals. 



Although a number of present day 

 workers are interested in the metabolism 

 of insects, we must note that the problem 

 is not a new one. Spallanzani (30) made 

 a number of observations on the larvae, 

 chrysalides, and adults of silkworms, 

 flies, bees, and wasps. He observed that 

 the respiratory exchanges of the larva 

 and imago were two or three times greater 

 than those of the chrysalid. His nu- 

 merical results have been branded as ' 'not 

 trustworthy," but we remember him as a 

 pioneer in this field of research. 



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