350
E. B. EDNEY
(direct and reflected), long-wave radiation, reflectivity of the animal's
surface, temperature, humidity and velocity of the air, and size and configuration of the animal's surface, to mention the most important ones, are
sometimes extremely difficult to measure accurately, and in any case may
vary from one minute to the next. It would therefore seem to be a waste of
time to try to deduce an animal's temperature from a knowledge of the
value of each of the parameters concerned, even though usable equations
are now available (Gates, 1962; Porter and Gates, 1969). On the other
hand, as Stower and Griffiths (1966) point out, it is desirable to construct
thermal balance sheets if only as a check to one's hypotheses. For example,
if we wish to know whether or not evaporation of water from a particular
arthropod is of significance in determining its body temperature, we can
get a lead by checking the relative importance of evaporation in a heat
balance sheet. For a review of the earlier work in this field, see Gunn
(1942) andEdney (1957).
In fact, the relative significance of each component varies greatly in
different circumstances. The contribution of metabolic heat in arthropods
is often negligible. However, if all other sources of energy flow are small,
as in an insect resting in the shade, or if the insect has a well-insulated
integument such as the furry covering of some moths and bees (Adams
and Heath, 1964a; Church, 1960), metabolic heat production may be very
significant. In a large hawk moth during flight, a thoracic temperature excess (above ambient) of 8°C has been measured and ascribed to metabolic
heat (see also below p. 352 for further measurements in Manduca), and
even in locusts the temperature excess during flight may amount to 7.1 °C
or more (Church, 1960; Weis-Fogh, 1967).
In direct solar radiation, metabolism and evaporation are, in insects,
relatively unimportant (Parry, 1951) and most of the heat loss occurs by
convection. Another factor of importance in direct sunlight is size. Larger
insects attain a higher temperature than smaller ones, and Digby (1955)
found experimentally that the temperature excess of locust-shaped insects
varies with the 0.4 power of the linear size, while for insects shaped like
bees or flies, the excess varies directly with linear size. Orientation to the
sun's rays may also affect temperature, as Fraenkel (1929), Kennedy
(1939), and more recently Stower and Griffiths (1966) have found for
locusts, and as I have observed in the tenebrionids, Onymacris rugatipennis
and O. brinki (Edney, 1971b). Air movement, by affecting the convection
component, is usually of major importance.
B. BODY TEMPERATURE AND THERMAL BALANCE
A good example of the modern approach is to be found in Stower and
Griffiths' (1966) work with the desert locust, Schistocerca. Using thermo-
E. B. EDNEY
(direct and reflected), long-wave radiation, reflectivity of the animal's
surface, temperature, humidity and velocity of the air, and size and configuration of the animal's surface, to mention the most important ones, are
sometimes extremely difficult to measure accurately, and in any case may
vary from one minute to the next. It would therefore seem to be a waste of
time to try to deduce an animal's temperature from a knowledge of the
value of each of the parameters concerned, even though usable equations
are now available (Gates, 1962; Porter and Gates, 1969). On the other
hand, as Stower and Griffiths (1966) point out, it is desirable to construct
thermal balance sheets if only as a check to one's hypotheses. For example,
if we wish to know whether or not evaporation of water from a particular
arthropod is of significance in determining its body temperature, we can
get a lead by checking the relative importance of evaporation in a heat
balance sheet. For a review of the earlier work in this field, see Gunn
(1942) andEdney (1957).
In fact, the relative significance of each component varies greatly in
different circumstances. The contribution of metabolic heat in arthropods
is often negligible. However, if all other sources of energy flow are small,
as in an insect resting in the shade, or if the insect has a well-insulated
integument such as the furry covering of some moths and bees (Adams
and Heath, 1964a; Church, 1960), metabolic heat production may be very
significant. In a large hawk moth during flight, a thoracic temperature excess (above ambient) of 8°C has been measured and ascribed to metabolic
heat (see also below p. 352 for further measurements in Manduca), and
even in locusts the temperature excess during flight may amount to 7.1 °C
or more (Church, 1960; Weis-Fogh, 1967).
In direct solar radiation, metabolism and evaporation are, in insects,
relatively unimportant (Parry, 1951) and most of the heat loss occurs by
convection. Another factor of importance in direct sunlight is size. Larger
insects attain a higher temperature than smaller ones, and Digby (1955)
found experimentally that the temperature excess of locust-shaped insects
varies with the 0.4 power of the linear size, while for insects shaped like
bees or flies, the excess varies directly with linear size. Orientation to the
sun's rays may also affect temperature, as Fraenkel (1929), Kennedy
(1939), and more recently Stower and Griffiths (1966) have found for
locusts, and as I have observed in the tenebrionids, Onymacris rugatipennis
and O. brinki (Edney, 1971b). Air movement, by affecting the convection
component, is usually of major importance.
B. BODY TEMPERATURE AND THERMAL BALANCE
A good example of the modern approach is to be found in Stower and
Griffiths' (1966) work with the desert locust, Schistocerca. Using thermo-