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V. G. DETHIER
parasitic wasps which have been studied is remarkably uniform. The
general pattern of behavior involves location of the host environment,
location of the host, a minute examination of the exterior of the host,
and a final appraisal of suitability after the ovipositor has been inserted.
The entire pattern of behavior consists of several easily recognizable
stages, the consummation of which depends upon reception of appropriate releasing stimuli. That the most important of these stimuli are
chemical in nature has been convincingly demonstrated. The elusiveness
of chemical stimuli has been no small factor in frustrating the experimenters who attempted to demonstrate the nature, presence, and role
of these stimuli in host-parasite relationships. That the problem is
amenable to scientific analysis is now universally acknowledged.
III. CHEMICAL TRAIL-FOLLOWING
The problem of orientation by terrestrial insects has been the subject
of extensive and ingenious experimentation for nearly two centuries.
The classical experiments of such eminent biologists as Bonnet (17791783), Lubbock (1884), Forel (1928), Bethe (1898), and Brun (1914,
1916), to mention only a few, were simple, straightforward, and convincing. The only difficulty was that they failed to agree. Indeed, the confusion which developed was so complete that workers in the field were
later driven to postulating varieties of mysterious sense perceptions not
experienced by man as well as such plausible but complicated mechanisms as a sense of angles, a muscular memory of the outgoing course
which, utilized in reverse, directed the homeward-bound insect (Pieron,
1904, 1912), and a topochemical sense whereby the insect by operating
the antennae as contact odor calipers makes use of a three-dimensional
spatial distribution of odors. The past few decades have witnessed the
reconciliation of the apparently conflicting results of earlier times and
the discovery that the true story is no less unbelievable than some of the
more bizarre hypotheses.
Bonnet had decided that ants laid down an odor trail. Approximately
one hundred years later Forel confirmed this fact. At this time, however, Lubbock came to the conclusion that the principal cue to orientation was a visual one; and Brun was able to demonstrate that a light
compass reaction to the sun was the most important single mechanism.
But Bethe (1898), unable to confirm Lubbock's results, concluded that
ants laid down a polarized odor trail of footprints. The confusion arose
from the circumstance that different investigators studied different species of ant and that different types of trail orientation exist.
A small terrestrial insect such as an ant traverses in the normal course
of its day an extremely rugged and extensive terrain spotted with nu-
V. G. DETHIER
parasitic wasps which have been studied is remarkably uniform. The
general pattern of behavior involves location of the host environment,
location of the host, a minute examination of the exterior of the host,
and a final appraisal of suitability after the ovipositor has been inserted.
The entire pattern of behavior consists of several easily recognizable
stages, the consummation of which depends upon reception of appropriate releasing stimuli. That the most important of these stimuli are
chemical in nature has been convincingly demonstrated. The elusiveness
of chemical stimuli has been no small factor in frustrating the experimenters who attempted to demonstrate the nature, presence, and role
of these stimuli in host-parasite relationships. That the problem is
amenable to scientific analysis is now universally acknowledged.
III. CHEMICAL TRAIL-FOLLOWING
The problem of orientation by terrestrial insects has been the subject
of extensive and ingenious experimentation for nearly two centuries.
The classical experiments of such eminent biologists as Bonnet (17791783), Lubbock (1884), Forel (1928), Bethe (1898), and Brun (1914,
1916), to mention only a few, were simple, straightforward, and convincing. The only difficulty was that they failed to agree. Indeed, the confusion which developed was so complete that workers in the field were
later driven to postulating varieties of mysterious sense perceptions not
experienced by man as well as such plausible but complicated mechanisms as a sense of angles, a muscular memory of the outgoing course
which, utilized in reverse, directed the homeward-bound insect (Pieron,
1904, 1912), and a topochemical sense whereby the insect by operating
the antennae as contact odor calipers makes use of a three-dimensional
spatial distribution of odors. The past few decades have witnessed the
reconciliation of the apparently conflicting results of earlier times and
the discovery that the true story is no less unbelievable than some of the
more bizarre hypotheses.
Bonnet had decided that ants laid down an odor trail. Approximately
one hundred years later Forel confirmed this fact. At this time, however, Lubbock came to the conclusion that the principal cue to orientation was a visual one; and Brun was able to demonstrate that a light
compass reaction to the sun was the most important single mechanism.
But Bethe (1898), unable to confirm Lubbock's results, concluded that
ants laid down a polarized odor trail of footprints. The confusion arose
from the circumstance that different investigators studied different species of ant and that different types of trail orientation exist.
A small terrestrial insect such as an ant traverses in the normal course
of its day an extremely rugged and extensive terrain spotted with nu-