356
E. B. EDNEY
Thus we have good evidence that in tsetse flies evaporative cooling does
regulate body temperature, but the question remains as to whether such
a comparatively small temperature depression is of survival value. At first
sight this would certainly seem to be unlikely, since the normal response
of an insect to high sublethal temperatures is to move away rather than
to lose precious water by regulating against them. However, some observations that I made in the field, with the help of J. Ford, suggest that in
certain circumstances the process might be of value. Measurements were
made in a tsetse fly area in Rhodesia at the hottest time of the year. Flies
observed to feed at a bait ox were marked, released, and subsequently
found in the vicinity resting on branches of trees and bushes, where, at
the hottest time of the day, they were exposed to air temperatures (measured precisely where the flies were sitting) of 38°C and above, the relative humidity lying between 25 and 3 5 % . Temperatures on the surface of
the bait animal at this time varied between 36°-37.5°C, in the shade and
40°-41.5°C when exposed to the sun. One reading of 47°C was obtained
on the animal's flank in the sun.
Tsetse flies are bound to feed (and during the process they inbibe warm
blood) so that they may occasionally be exposed for short periods to conditions in which an ability to drop the body temperature is critical for
survival.
VI. Morphological Adaptations, Including Surface Color
A very useful and beautifully illustrated discussion of the interaction
of evolutionary history and present habits and habitats in psammophilous
tenebrionid beetles is given by Koch (1961).
Some of the morphological modifications described as being adaptive
for desert life are, in fact, adaptive to a psammophilous existence. One
has only to compare the flat, plate-like structure of Arenivaga (Fig. 12)
or the tenebrionid beetle, Lepidochora porti, with the long spindly-legged
Onymacris plana to recognize that the former is highly adaptive to swimming through sand, the latter to running rapidly over the hot surface (Koch,
1961). The legs of endopsammophilous forms are usually modified by
the development of flat oarlike surfaces or large clawlike spines (Fig. 18),
associated with digging in sand or swimming through it. Tinkham (1965,
1968, and earlier papers) has described several such adaptations in
crickets and other sand dune insects.
An even closer approximation to swimming is shown by a therevid fly
larva from the dunes of southern California which moves below the surface
with a typical undulatory swimming action. It leaves the track shown in
the bottom of Fig. 12b.
E. B. EDNEY
Thus we have good evidence that in tsetse flies evaporative cooling does
regulate body temperature, but the question remains as to whether such
a comparatively small temperature depression is of survival value. At first
sight this would certainly seem to be unlikely, since the normal response
of an insect to high sublethal temperatures is to move away rather than
to lose precious water by regulating against them. However, some observations that I made in the field, with the help of J. Ford, suggest that in
certain circumstances the process might be of value. Measurements were
made in a tsetse fly area in Rhodesia at the hottest time of the year. Flies
observed to feed at a bait ox were marked, released, and subsequently
found in the vicinity resting on branches of trees and bushes, where, at
the hottest time of the day, they were exposed to air temperatures (measured precisely where the flies were sitting) of 38°C and above, the relative humidity lying between 25 and 3 5 % . Temperatures on the surface of
the bait animal at this time varied between 36°-37.5°C, in the shade and
40°-41.5°C when exposed to the sun. One reading of 47°C was obtained
on the animal's flank in the sun.
Tsetse flies are bound to feed (and during the process they inbibe warm
blood) so that they may occasionally be exposed for short periods to conditions in which an ability to drop the body temperature is critical for
survival.
VI. Morphological Adaptations, Including Surface Color
A very useful and beautifully illustrated discussion of the interaction
of evolutionary history and present habits and habitats in psammophilous
tenebrionid beetles is given by Koch (1961).
Some of the morphological modifications described as being adaptive
for desert life are, in fact, adaptive to a psammophilous existence. One
has only to compare the flat, plate-like structure of Arenivaga (Fig. 12)
or the tenebrionid beetle, Lepidochora porti, with the long spindly-legged
Onymacris plana to recognize that the former is highly adaptive to swimming through sand, the latter to running rapidly over the hot surface (Koch,
1961). The legs of endopsammophilous forms are usually modified by
the development of flat oarlike surfaces or large clawlike spines (Fig. 18),
associated with digging in sand or swimming through it. Tinkham (1965,
1968, and earlier papers) has described several such adaptations in
crickets and other sand dune insects.
An even closer approximation to swimming is shown by a therevid fly
larva from the dunes of southern California which moves below the surface
with a typical undulatory swimming action. It leaves the track shown in
the bottom of Fig. 12b.