164
V. G. DETHIER
Bethe believed that trail-following in response to a specific chemical was
automatic. If colony odor and trail odor are identical the alternatives are
that the response to trails is automatic or that the ant becomes conditioned to the odor in the nest before venturing out on to the trail. In
studying this question in the army ant, Schneirla observed that callows
of E. hamatum became fairly able trail-followers in four to five days
after hatching. Earlier, they are hesitant blunderers who impede the
progress of hurrying foragers. If, however, pupae are removed from the
nest before metamorphosis, the callows upon emergence are less well
able to follow trails than their companions who were left in the nest.
This observation suggests that the callows become conditioned to the
trail odor while still in the nest. Schneirla postulated a rudimentary
learning process of the habituation type and pointed out that this hypotheses is consistent with a theory for social insects in general which
takes into account the importance of early environment and activities for
the development of social reaction patterns (Schneirla, 1944).
Trail-following by solitary insects, especially others than Hymenoptera, has not been investigated in any great detail.
Since Fabre's
(1919) classic description of trail-following of the processionary moth
larvae (Cnethocampa
processionaria),
types of trail-following by many
lepidopterous larvae have been described. For the most part the orientation is accomplished by tactile response to silken threads laid down by
one or more of the advancing larvae. There is no conclusive evidence that
a chemical trail exists. Marshall's (1904) observations have been quoted
as evidence that there is a chemical trail laid down by larvae of the
moth Hemileuca maia. He noted that breaking of the thread on the trail
did not stop the column of larvae from continuing on but that breaking
with a finger dipped in water, the break then being wiped dry, did stop
the procession. The first response could easily have been the results of
the larvae's ability to maintain a heading as some ants do; the second
experiment did not really rule out the possibility of a repellent odor
from the finger. A reinvestigation would be desirable.
Insects which do not ordinarily make or follow trail can be forced
under certain experimental conditions to follow an artificial trail composed of a food substance. For example, larvae of many Lepidoptera
can be made to follow a narrow trail of sugar solution across the top
of a table, eating as they go. Muscoid Díptera, as exemplified by the
blowfly Phormia regina, can follow the most intricate trail of sugar until
they become sated. In the process they employ the tarsi and extended
proboscis. Random wandering brings the fly to the trail, which is first
perceived by the tarsal chemoreceptors. The proboscis is extended and
the fly orients itself along the longitudinal axis of the trail as it feeds.
V. G. DETHIER
Bethe believed that trail-following in response to a specific chemical was
automatic. If colony odor and trail odor are identical the alternatives are
that the response to trails is automatic or that the ant becomes conditioned to the odor in the nest before venturing out on to the trail. In
studying this question in the army ant, Schneirla observed that callows
of E. hamatum became fairly able trail-followers in four to five days
after hatching. Earlier, they are hesitant blunderers who impede the
progress of hurrying foragers. If, however, pupae are removed from the
nest before metamorphosis, the callows upon emergence are less well
able to follow trails than their companions who were left in the nest.
This observation suggests that the callows become conditioned to the
trail odor while still in the nest. Schneirla postulated a rudimentary
learning process of the habituation type and pointed out that this hypotheses is consistent with a theory for social insects in general which
takes into account the importance of early environment and activities for
the development of social reaction patterns (Schneirla, 1944).
Trail-following by solitary insects, especially others than Hymenoptera, has not been investigated in any great detail.
Since Fabre's
(1919) classic description of trail-following of the processionary moth
larvae (Cnethocampa
processionaria),
types of trail-following by many
lepidopterous larvae have been described. For the most part the orientation is accomplished by tactile response to silken threads laid down by
one or more of the advancing larvae. There is no conclusive evidence that
a chemical trail exists. Marshall's (1904) observations have been quoted
as evidence that there is a chemical trail laid down by larvae of the
moth Hemileuca maia. He noted that breaking of the thread on the trail
did not stop the column of larvae from continuing on but that breaking
with a finger dipped in water, the break then being wiped dry, did stop
the procession. The first response could easily have been the results of
the larvae's ability to maintain a heading as some ants do; the second
experiment did not really rule out the possibility of a repellent odor
from the finger. A reinvestigation would be desirable.
Insects which do not ordinarily make or follow trail can be forced
under certain experimental conditions to follow an artificial trail composed of a food substance. For example, larvae of many Lepidoptera
can be made to follow a narrow trail of sugar solution across the top
of a table, eating as they go. Muscoid Díptera, as exemplified by the
blowfly Phormia regina, can follow the most intricate trail of sugar until
they become sated. In the process they employ the tarsi and extended
proboscis. Random wandering brings the fly to the trail, which is first
perceived by the tarsal chemoreceptors. The proboscis is extended and
the fly orients itself along the longitudinal axis of the trail as it feeds.