166
V. G. DETHIER
1954, 1955). The distance over which these scents are effective is open
to question, although admittedly it may be great. Götz (1951) is probably correct in believing that the effective distances have been exaggerated. Those reported vary from 1.5 cm. (Roth and Willis, 1952b) in the
case of the webbing clothes moth \Ύ inedia biselliella (Hum.)] to 12
km. in the case of certain bombycids (see Teuber, 1954). The importance of these distances lies in their bearing on the mechanism of action
of the material. Although marked moths have been employed in distance determinations in many instances, it remains to be seen how many
of the returns resulted from actual stimulation by the scent, how many
were in response to air currents alone, and how many represented random straying back into an area which was within the effective range
of the scent. It is clearly possible that the effective distance could be
much shorter and that moths reached the periphery of the effective area
without direct chemical orientation.
The question of the nature of the guiding stimulus in this behavior
has gone through a full cycle of interpretation. Just as trail-following
by ants was at one time thought to depend upon mysterious senses
beyond the knowledge and experience of man, so assembling by male
Lepidoptera was at one time believed to depend upon mysterious radiations of one sort or another. The invocation of radiation stemmed from
a belief that the distances over which the stimulus operated were
incredibly great and that only some type of radiation could remain in
effective intensity over these distances. The same arguments are being
advanced again today. In the meantime the evidence for the intervention of air currents and olfaction had been accumulating, and most
people believe that the female generates molecules of a volatile material
which are disseminated by the wind and together with the stimulation
by air currents make orientation possible.
Before considering the mechanism of orientation, mention should be
made of the proposals running counter to the ideas expressed in the
sentence above. These are set forth by Teudt (1919), Barth (1937), and
Teuber (1954), and have been reviewed by Götz (1951). The consensus
of these opinions is that the quantity of odorous material produced and
the distance over which it operates preclude a sufficiently large number
of molecules from impinging on the sense organs of the male. Teuber
(1954), for example, has calculated that in the case of Bombyx mori the
concentration of stimulus is of the order of one molecule per cubic centimeter of air at the site of action. This calculation is based on the following considerations. The sex attractant of B. mori, as isolated by
Butenandt (1940, 1941), has a molecular weight of 254 and the empirical
formula Ci 6 H 3 o0 2 . From 7000 females one obtains 100 mg. of material,
V. G. DETHIER
1954, 1955). The distance over which these scents are effective is open
to question, although admittedly it may be great. Götz (1951) is probably correct in believing that the effective distances have been exaggerated. Those reported vary from 1.5 cm. (Roth and Willis, 1952b) in the
case of the webbing clothes moth \Ύ inedia biselliella (Hum.)] to 12
km. in the case of certain bombycids (see Teuber, 1954). The importance of these distances lies in their bearing on the mechanism of action
of the material. Although marked moths have been employed in distance determinations in many instances, it remains to be seen how many
of the returns resulted from actual stimulation by the scent, how many
were in response to air currents alone, and how many represented random straying back into an area which was within the effective range
of the scent. It is clearly possible that the effective distance could be
much shorter and that moths reached the periphery of the effective area
without direct chemical orientation.
The question of the nature of the guiding stimulus in this behavior
has gone through a full cycle of interpretation. Just as trail-following
by ants was at one time thought to depend upon mysterious senses
beyond the knowledge and experience of man, so assembling by male
Lepidoptera was at one time believed to depend upon mysterious radiations of one sort or another. The invocation of radiation stemmed from
a belief that the distances over which the stimulus operated were
incredibly great and that only some type of radiation could remain in
effective intensity over these distances. The same arguments are being
advanced again today. In the meantime the evidence for the intervention of air currents and olfaction had been accumulating, and most
people believe that the female generates molecules of a volatile material
which are disseminated by the wind and together with the stimulation
by air currents make orientation possible.
Before considering the mechanism of orientation, mention should be
made of the proposals running counter to the ideas expressed in the
sentence above. These are set forth by Teudt (1919), Barth (1937), and
Teuber (1954), and have been reviewed by Götz (1951). The consensus
of these opinions is that the quantity of odorous material produced and
the distance over which it operates preclude a sufficiently large number
of molecules from impinging on the sense organs of the male. Teuber
(1954), for example, has calculated that in the case of Bombyx mori the
concentration of stimulus is of the order of one molecule per cubic centimeter of air at the site of action. This calculation is based on the following considerations. The sex attractant of B. mori, as isolated by
Butenandt (1940, 1941), has a molecular weight of 254 and the empirical
formula Ci 6 H 3 o0 2 . From 7000 females one obtains 100 mg. of material,