CHEMORECEPTION 125 



although the conspecific gland tends to elicit the largest response 

 (Schneider, 1962). 



Recently Morita and Yamashita (1961) have been able to record 

 directly from a simple large sensiHum basiconicum on the antenna of 

 the larva of Bombyx mori. This had been shown to be an olfactory 

 organ innervated by approximately twenty neurons (Dethier, 1941). 

 When odours of substances contained in the essential oil of mulberry 

 leaves (e.g., Py-hexanol and /z-butylaldehyde) were applied to the sen- 

 sillum a slow negative potential accompanied by an increase in action 

 potential frequency occurred. Some compounds evoked a slow diph- 

 asic potential, from negative to positive, while anaesthetics evoked 

 slow positive potentials accompanied by a decrease in impulse fre- 

 quency. A complete interpretation of these results is rendered difficult 

 by the fact that the sensillum is multiply innervated; however, the 

 available evidence strongly suggests that the slow negative potential 

 evoked by naturally occurring food substances is a true receptor 

 potential. 



Odour Qualities 



It is clear from studies of attractants and repellents that for all insects 

 there are at least two odour modaUties, that is, 'acceptable' and 

 'unacceptable', but it is unlikely that these represent accurately the 

 olfactory world of insects. For many insects that respond in a highly 

 specific manner to one particular odour, as, for example, the male 

 silkworm to female sex-attractant, and many monophagous cater- 

 pillars to the odour of their one food-plant, it is possible that the ol- 

 olfactory receptors are tuned only to that odour. Electrophysiological 

 recordings from the antennae of male Bombyx mori thus far have not 

 revealed a sensitivity to any compound other than the natural and 

 synthetic sex attractants of Bombyx and the natural attractants of 

 closely related species (Schneider, 1962). 



The honeybee, on the other hand, is obviously sensitive to many 

 odours, but does it confuse them as one or can it discriminate? By 

 training bees to associate a particular odour with food, von Frisch 

 (1919) was able to show that a number of odours were discriminated. 

 Furthermore, compounds with different structure, which to man 

 possessed similar odours, were confused as one by the bee, whereas 

 compounds with nearly identical structure but obviously different 

 odours were easily distinguished. Within the following pairs the two 

 members are easily distinguished by the bee : amyl acetate and methyl 

 heptenone, bromstyrol and phenylacetaldehyde, isobutyl benzoate 



