126 THE PHYSIOLOGY OF INSECT SENSES 



and salicylic acid amyl ester, /?-cresol methyl ether and w-cresol 

 methyl ether. 



CONTACT CHEMORECEPTION 

 Sensitivity 



Many behavioural studies have been conducted with numerous species 

 of insects for the purpose of locating and mapping contact chemore- 

 ceptors, determining limits of qualities, and elucidating the nature of 

 receptor action. These studies, centred for the most part around feed- 

 ing behaviour, have usually been designed as measurements of accept- 

 ance and rejection thresholds. Extension of the proboscis, duration of 

 feeding, and measurement of crop loads have been a few of the criteria 

 employed (for details consult Dethier and Chadwick, 1948 a). 



Table 4 



(From Dethier and Chadwick, 1948 a) 



Comparison of taste thresholds 



Compound 



Threshold Concentrations 



Sucrose 



Sodium chloride 



Hydrochloric 



acid 

 Quinine 



Man, 0-02M; bee, 0-06-0-125M; butterfly (Pyrameis), 

 average ca. 0-OlM, in starvation as little as 

 8 X IQ-^M; Danaus,9'S x lO-^M;hoTSQfiy(Tabanus) 

 0005-0 IIM. 



Man, 0-009M; bee, rejects ca. 0-24M in 0-5M sucrose; 

 various caterpillars reject at 0-2M, whereas others 

 accept over the full range up to and including 5 -OM. 



Man, 000125M; bee, rejects OOOIM in 1 OM sucrose; 

 various caterpillars reject at 0-01-0-2M. 



Man, 1 -5 x 10" "^M; bee , rejects at 8 x 10"* in 1 -OM 

 sucrose; various caterpillars reject at 0002-0-033M; 

 aquatic beetles were conditioned to respond to 

 1-25 X lO-^M. 



Data on man are for specific thresholds, adapted from Moncrieff" (1944); 

 for the bee, from von Frisch (1934); for Pyrameis, from Minnich (1922); 

 for Danaus, from Anderson (1932); for caterpillars, from Eger (1937); for 

 aquatic beetles, from Bauer (1938). The figures for insects are thresholds 

 of response. 



Threshold studies have revealed many of the characteristics of the 

 contact chemical sense. They have shown, for example, that the 

 thresholds are frequently lower than those of man for similar sub- 

 stances (Table 4). They have revealed among individuals differences 

 that follow a common pattern. For example, the scattering of 



