CHAPTER V 



Chemoreception 



The accomplishment of many sexual, reproductive, social, and feeding 

 activities of insects depends to a great extent upon the detection and 

 assessment of specific chemical aspects of the environment. With the 

 exception of feeding, where most of the chemical energy of the stimu- 

 lating materials is utilized for purposes remote from the activity of the 

 sense organ, the energy of compounds eliciting the other behaviour 

 patterns serves merely to trigger excitation in receptors. 



These receptors are not chemosensitive simply because of fortuitous 

 anatomical location, or exposure to the environment, or the possess- 

 ion of permeable coverings (Dethier, 1962). On the contrary, they are 

 inherently highly specialized and specific. Because of their specificity it 

 v^ould probably be more meaningful to speak of salt, sugar, or sex- 

 attractant receptors than of olfactory and contact chemoreceptors ; 

 however, since our knowledge of their physiology is still fragmentary, 

 the two broad but ambiguous categories are still convenient (cf. 

 Dethier and Chadwick, 1948 a). 



It was postulated long before being demonstrated that chemo- 

 receptors generated impulses as did other receptors. There is nothing 

 unique about this part of the train of events initiated by stimulation. 

 At the opposite end of the train, a beginning is being made towards an 

 understanding of the behavioural correlates (cf., e.g., Dethier, 1957). 

 The great unknown now is the basis of specificity and the nature of the 

 transducing mechanism (Dethier, 1956, 1962). 



THE RECEPTORS 



The identification of chemoreceptors (whose nature is never so obvious 

 as that of photoreceptors and sound receptors) has probably been 

 retarded more than that of any other sense modality by the tendency to 

 assign the function of chemoreception to all sensilla whose structure 

 conforms to some postulated norm. There is, therefore, a voluminous 

 literature on the structure of chemoreceptors real and supposed (for 

 detailed reviews consult Kraepelin, 1833; Rohler, 1906; Forel, 1908; 

 Mclndoo, 1914 a, 1914 b; von Frisch, 1921; Minnich, 1929 a; Mar- 

 shall, 1935; Dethier and Chadwick, 1948 a; Dethier, 1953). 



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