ELECTROPHYSIOLOGICAL INVESTIGATION 101 



able to make highly sensitive intensity discriminations. But such dis- 

 criminations must be optional in the higher range, where response rises 

 steeply with concentration. These higher concentrations are about equal 

 to the experimentally determined output of a female gland. The Bombyx 

 sex attractant (Bombykol) is usually more effective than its geometrical 

 isomers. The d- and /-form of the Porthetria sex attractant, as well as the 

 dl racemic mixture, are equally effective. 



In no case studied so far did the attracting substances of any of the 

 female moths elicit a response in the antennae of any of the female of 

 these same species. 



The lure substance of Bombyx and Porrhetria did not elicit electrical 

 responses in cross-stimulation experiments. However, Bombyx males 

 react with weak electrical responses to some glands of the Saturniids and 

 with weak behavioural responses to females of Porthetria and several 

 Saturniids. In one of the Saturniid-subfamilies no species or genus 

 specificity of the attracting substances could be found. 



Since the present state of our knowledge on many aspects of insect 

 olfaction is still very scant, it is perhaps worthwhile to define some areas 

 in which intensive investigation is necessary : 



1. Determination of the identity and physiological range of the receptor 

 cells responsible for the different chemical modalities as well as sub- 

 sequent analysis of the fine structure and chemical composition of 

 the receptor cell membrane. 



2. Further elucidation of the sequence of processes taking place in the 

 primary sensory cell under the influence of stimulating molecules. 

 For the electro-physiologist this involves a detailed study of receptor 

 membrane responses and generation of nerve impulses. The trans- 

 duction of " chemical energy " into graded potentials also has to be 

 clarified. 



3. Analysis of the structure and biochemistry of the lure gland. This 

 " emitting " system can be compared analogously to the presynaptic 

 nerve fibre. Bombykol is then the transmitter substance, eliciting 

 electrogenesis in the olfactory receptor membrane (see Fig. 10). 



4. Detailed study of the way in which an insect orients under the 

 influence of olfactory stimuli. Here information from the olfactory 

 sense must be integrated with information from other sensory 

 modalities. 



ACKNOWLEDGEMENTS 



The original work was supported by the Deutsche Forschungsgemein- 

 schaft. — Prof. A. Butenandt and Dr. E. Hecker (Munich) kindly supplied 

 the 56>/77/7>'.v-attracting substances. — Dr. M. Jackson (Beltsville) kindly 



