ELECTROPHYSIOLOGICAL INVESTIGATION 



97 



impulses are rarely picked up. Recording from only a very few cells in the 

 sensory epithelium (see Schneider, 1957) will bring nerve impulses of rather 

 large size into the picture. 



Similar electrophysiological experiments to the ones described with 

 Bombyx have been done recently on a smaller scale with the gypsy moth, 



Fig. 9. The electrophysiological (EAG) stimulus-response curve of Porthetria 

 dispar males to the optical isomers of acetoxyhexadecenol. The broken line 

 represents the response curve to the <:/-isomer ; the solid line represents the 

 response curve to the /-isomer. Illustrated is a typical experiment performed 

 with one animal and one electrode position (from Boeckh and Schneider, 



unpublished). 



Porthetria dispar (Block and Schneider, unpublished). As far as our in- 

 formation goes, the situation is much less complex than with Bombyx. The 

 Porthetria male antenna studied with the EAG method shows the expected 

 stimulus-response curve (Fig. 9). It rises with ascending concentrations 

 first slowly and more sharply later. A saturation effect has not been 

 observed, even with pure attractant in the highest concentration tested. 



The gypsy moth sexual attracting substance is optically active and exists 

 in a d- or dextrorotatory and an /- or levorotatory form. No activity dif- 

 ferences between the two isomers could be found when checked with the 

 EAG method. The same also seems to be true behaviourally since brief 

 but informative tests showed little difference between the d- and the /-form. 

 Also, we compared freshly dissected female glands of Porthetria dispar 

 with known concentrations of lure substances on paper and found that the 

 gland corresponds to about 0.05//g of attractant on paper. 



Usually the sexual lure substances of moths are called species-specific. 



