98 DIETRICH SCHNEIDER 



That this is not necessarily so has already been demonstrated by behavioural 

 tests (for literature see Schneider, 1962). Our information indicates that 

 specificity may only reach to the family or sub-family level, as in the case of 

 the Saturniids (Schneider, 1962). However, there is no EAG-response 

 above control when the Bombyx male antenna is stimulated with the 

 Porthetria lure gland or natural or synthetic substances and vice versa. 

 While Porthetria males in behavioural tests are completely uneflfected by 

 virgin Bombyx females, the reverse is not true. The Bombyx males give a 

 weak but definite response to the other species. Unfortunately, it was not 

 yet possible to compare electrophysiologically the two well known Por- 

 thetria species, dispar and monacha. Behaviour tests by Schwinck (1955) 

 demonstrated clearly that females of both species attract the males of the 

 other. 



While we did not expect a female moth to show any motor reaction 

 when confronted with its own lure substance in high concentration, it was 

 surprising to find that the Bombyx female antenna gave no EAG response 

 to the gland or to synthesized Bombykol. Since such a female antenna was 

 able to react to other odorous substances in the same way as the male 

 antenna, it was concluded that the female moth does not have the specific 

 receptor type for detecting its own perfume. Humans also cannot detect 

 Bombykol, no matter how high the attractant concentration. The in- 

 ability of the female moth to identify its own lure substance was also found 

 in the Saturniids (Schneider, 1962) and more recently for the gypsy moth. 

 The antennae of the female moths do not even have receptors to detect 

 substances of the same " class " of attracting compounds. None of the 

 female glands of Bombyx and of the Saturniids studied so far had an 

 effect upon any of the antennae of the female donors. Recently we checked 

 the antennae of female Bombyx mori, Porthetria dispar and Antheraea 

 pernyi (Saturniidae) during stimulation with the female lure glands of all 

 three females and could not record olfactory EAG's, although other scents 

 aff'ected the antennae (Block and Schneider, unpublished). 



The threshold concentrations, given in absolute amounts of lure sub- 

 stance, make it possible to calculate the number of molecules expected 

 on the glass rods or filter papers used as stimulus sources. At the lowest 

 Bombykol threshold determined with the EAG method (lO'^Vg o^i the 

 144 mm^ piece of filter paper) there are only 10'^ molecules on the paper. 

 The vapour pressure of Bombykol, although not yet determined, is pro- 

 bably not very high. Therefore, only a fraction of the available molecules 

 actually leaves the filter paper during the stimulation time of 1-2 sec. 

 These molecules are carried in a certain volume of air (3 / of air/min) 

 which streams over the antenna. Without knowledge of the vapour pres- 

 sure, it is impossible to make any precise calculations of the Bombykol- 

 density at threshold, but it seems plausible to think of a rather small 



