118 THE PHYSIOLOGY OF INSECT SENSES 



Table 2 



(From Schwarz, 1955) 



Olfactory thresholds for man and various insects 



Hoskins, 1939; Dethier, 1941; Crombie, 1944; Dethier and Yost, 

 1952; Hodgson, 1953; Schwarz, 1955; Fischer, 1957; Dostal, 1958; 

 and others [see Dethier, 1947 b] ). A few data are given for comparison 

 in Tables 1 and 2. 



Attempts have been made to correlate the acuity of olfaction in the 

 various species with the numbers of sensilla, but the correlation is 

 highly conjectural in as much as the identity of the receptors is un- 

 certain in many species, and quantitative tests of acuity have not been 

 undertaken. It is certainly true that some correlation exists between 

 the number of receptors and behavioural response to odours. The 

 number of olfactory sensilla in an insect varies from species to species. 

 There may be as few as 9-10, as in the human louse, or there may be 

 as many as 30,000 in the drone honeybee (Schenk, 1903 ; Vogel, 1923 b; 

 Mclndoo, 1914a, 1914b). Lice and lepidopterous larvae, which live 

 on their hosts and have little apparent need for an extremely acute 

 olfactory sense, possess few sensilla. In the life of the honeybee, on the 

 other hand, many odours are encountered and are highly significant. 



