CHEMORECEPTION AND THE BEHAVIOR OF INSECTS
165
If the trail is wide, guidance is achieved chiefly through the tarsi, the
fly turning back to the trail every time the tarsi are no longer stimulated.
If the trail is so narrow as to pass beneath the fly's body between the
legs, orientation is achieved by probing with the proboscis. These observations indicate that a species which is not ordinarily a trail-follower
can follow a chemical trail without conditioning or learning.
The chemical trails of ants have been called odor trails by most
authors. Presumably the basis for this appellation is the fact that the
principal organs employed in trail orientation are the antennae; however
it has been shown (Kunze, 1933, and others) that many Hymenoptera
possess contact chemoreceptors as well as olfactory receptors on the antennae. This is not the occasion to enter into a discussion of the distinctions between olfaction and contact chemoreception (see Dethier and
Chadwick, 1948; Jahn and Wulff, 1950), and the question of what
category of sense perception the trails stimulate may be without meaning.
The experiments with flies do show, however, that chemical trails in
which the stimulus is nonodorous may be followed efficiently. As trailing
by dogs proves, it is equally clear that odor also is an effective medium
for trail orientation (cf., e.g., Johnson, 1914). For a recent review the
work of Vowles (1955) should be consulted.
IV. ORIENTATION BY FLYING INSECTS
Air-borne odors emanating from food and from special glands on the
females of some insects, notably moths and butterflies, are the attractants by means of which individuals find their way to mates and sustenance. The methods whereby this orientation is accomplished have
until recently been the object of more speculation than experimentation.
A current revival of interest in assembling, as the orientation by male
moths to females is termed, may result in the instigation of sufficiently
carefully controlled physiological experiments to give us further insight
into the remarkable action of these sex attractants. The entire subject
has recently been reviewed by Götz (1951). Briefly, the well known
story is this. Males of many moths and butterflies orient to the females
of the species with the help of odorous materials disseminated by the
females. Special glands in intersegmental folds of the female's seventh
and eighth abdominal segments are the source of this material, which
is attractive in all concentrations above threshold (i.e., there is no repellent concentration) and which is imperceptible by man. The male
is able to pick out this scent from a melange of others more concentrated. The degree of specificity varies. In some cases the scent is attractive to congeners; in others it is specific for strains of the same
species (see Barth, 1937; Görnitz, 1949; Götz, 1951; Schwinck, 1953,
165
If the trail is wide, guidance is achieved chiefly through the tarsi, the
fly turning back to the trail every time the tarsi are no longer stimulated.
If the trail is so narrow as to pass beneath the fly's body between the
legs, orientation is achieved by probing with the proboscis. These observations indicate that a species which is not ordinarily a trail-follower
can follow a chemical trail without conditioning or learning.
The chemical trails of ants have been called odor trails by most
authors. Presumably the basis for this appellation is the fact that the
principal organs employed in trail orientation are the antennae; however
it has been shown (Kunze, 1933, and others) that many Hymenoptera
possess contact chemoreceptors as well as olfactory receptors on the antennae. This is not the occasion to enter into a discussion of the distinctions between olfaction and contact chemoreception (see Dethier and
Chadwick, 1948; Jahn and Wulff, 1950), and the question of what
category of sense perception the trails stimulate may be without meaning.
The experiments with flies do show, however, that chemical trails in
which the stimulus is nonodorous may be followed efficiently. As trailing
by dogs proves, it is equally clear that odor also is an effective medium
for trail orientation (cf., e.g., Johnson, 1914). For a recent review the
work of Vowles (1955) should be consulted.
IV. ORIENTATION BY FLYING INSECTS
Air-borne odors emanating from food and from special glands on the
females of some insects, notably moths and butterflies, are the attractants by means of which individuals find their way to mates and sustenance. The methods whereby this orientation is accomplished have
until recently been the object of more speculation than experimentation.
A current revival of interest in assembling, as the orientation by male
moths to females is termed, may result in the instigation of sufficiently
carefully controlled physiological experiments to give us further insight
into the remarkable action of these sex attractants. The entire subject
has recently been reviewed by Götz (1951). Briefly, the well known
story is this. Males of many moths and butterflies orient to the females
of the species with the help of odorous materials disseminated by the
females. Special glands in intersegmental folds of the female's seventh
and eighth abdominal segments are the source of this material, which
is attractive in all concentrations above threshold (i.e., there is no repellent concentration) and which is imperceptible by man. The male
is able to pick out this scent from a melange of others more concentrated. The degree of specificity varies. In some cases the scent is attractive to congeners; in others it is specific for strains of the same
species (see Barth, 1937; Görnitz, 1949; Götz, 1951; Schwinck, 1953,