Metabolic activity and water vapour absorption in the mealworm Tenebrio molitor L. (Coleoptera, Tenebrionidae): real-time measurements by two-channel microcalorimetry
Department of Life sciences and Chemistry, Roskilde University, DK-4000 Roskilde, Denmark
* Authors for correspondence (e-mail: hr{at}ruc.dk, pwesth{at}ruc.dk)
Accepted 24 October 2003
![]() |
Summary |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The metabolic heat production of the larvae was 5-6 J h-1 g-1 wet mass in the initial part of the experiment. However, this value doubled 2-3 h prior to the onset of WVA, when the RH had reached 88%. This increase in metabolic heat production gradually tapered off over the following 24 h of WVA, during which time WVA remained high. Animals exposed to RH protocols that did not induce WVA showed no such anomalies in metabolic heat flow. This may suggest that the increased metabolism reflects the preparation of the WVA apparatus. Finally, the method was used to quantify water losses in the microgram range associated with wriggling and tracheal ventilation.
Key words: water exchange, specific corrected metabolic heat flux, controlled relative humidity, water vapour absorption threshold, mealworm, Tenebrio molitor
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Since early studies by Buxton
(1930) and Mellanby
(1932
), gravimetric methods
have been most commonly used for measuring evaporative water loss in
arthropods (Audsley et al.,
1993
; Hadley,
1994
; Pelletier,
1995
; Ramløv and Lee,
2000
). This method assumes that mass loss and water loss are
equivalent (Wharton and Richards,
1978
). Changes in body mass are usually recorded at fixed
intervals under known conditions of temperature and humidity
(Beament, 1959
;
Dunbar and Winston, 1975
;
Edney, 1971
; Machin,
1975
,
1976
,
1978
;
Machin and O'Donnell, 1991
;
Noble-Nesbitt, 1978
;
Pelletier, 1995
). These
measurements are often done in static systems with no air movement, which may
cause water vapour gradients within the container housing the animal
(Hadley, 1994
).
Gravimetrically determined water flux, however, is susceptible to certain
errors, particularly the disruption of experimental temperatures and relative
humidity (RH) during weighing (Hadley,
1994
). Machin
(1976
) designed a flow-through
system in which it was possible to simultaneously weigh the test animal and
control the RH and temperature in the balance chamber, which solved the
problems due to disruption when weighing the animals. More recently,
flow-through respirometry has been used to measure CO2 and water
vapour production simultaneously in arthropods
(Gibbs et al., 1998
;
Williams et al., 1998
). This
experimental set-up requires temporary perfusion with dry air, which may
induce a response from the experimental animal. Other investigators have
developed a method to measure water loss isotopically
(Wharton and Richards, 1978
).
However, the injection of tritiated solutions into animals introduces problems
due to the puncture of the cuticle causing stress and wounds that must be
treated. Water loss rates obtained isotopically are in principle
unidirectional effluxes, and hence often slightly higher than the net changes
determined gravimetrically (Hadley,
1994
). Another possible limitation of isotope methods is the
compartmentalisation of tritium in the arthropod
(Hadley, 1994
).
Calorimetry is used extensively for metabolic studies in animals
(Dauncey, 1991; Harak et al.,
1996
,
1998
,
1999
;
Kuusik et al., 1994
;
Lambrecht, 1998
; Schmolz et
al., 1999
,
2002
;
Schmolz and Lambrecht, 2000
;
Schaatschmidt et al., 1995
).
Some of these studies use calorimetric measurements to monitor the heat flux
from the animals at prefixed temperature and/or humidity. In some cases, the
measurement of heat flow is supplemented by the simultaneous measurements of
oxygen consumption (Harak et al.,
1996
,
1999
). Most work in this field
is performed on so-called isothermal microcalorimeters, implying instruments
designed for work in the microwatt range under isothermal conditions
(Guan et al., 1999
;
Johansson and Wadsö,
1999
). In many cases, the versatility of the technique has been
enhanced by the insertion of miniaturized analytical sensors into the reaction
vessel, thus improving the interpretation of the results
(Bäckman and Wadsö,
1991
).
In this work we introduce a method combining two calorimeters, which
enables the simultaneous quantification of water exchange and heat production
of an experimental animal. Calorimetric approaches to vapour sorption have
previously been presented by Wadsö and Wadsö
(1996,
1997
) and Markova and
Wadsö (1999
), and a
methodology similar to the one employed here has previously been used for
studies of the hydration of compounds of pharmaceutical interest
(Lehto and Laine, 2000
).
In the present study the twin calorimetric method is used to examine water exchange and related metabolic heat production in drought-stressed larvae of T. molitor. The results indicate that an increase in metabolism prior to the initiation of water vapour absorption reflects a sensory response to the RH of the experimental chamber.
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Instrumentation
The calorimetric measurements were conducted on a thermal activity monitor
(TAM) 2277 isothermal calorimeter (Thermometric A/B, Järfälla,
Sweden) equipped with an amplifier module enabling a resolution of the heat
flow measurements extending into the nW range. The instrument has a total of
four calorimetric channels, each of which consists of a sample cell and a
reference cell mounted in a separate heat sink. This design allows independent
measurement of the differential (sample - reference) heat flow in each
channel, with the only restriction that the experimental temperature is the
same (since all four heat sinks are in the same water bath). During
measurement, the primary observable variable is simply the temperature
difference between the sample and the reference; through appropriate
calibration this translates into the sample-to-reference heat flow (in W).
Details of a very similar, albeit less sensitive, version of this equipment
have been published by its inventors
(Suurkuusk and Wadsö,
1982).
In the current application, one type 2250 perfusion module (Thermometric) with a 1 ml stainless steel cell, and one type 2250 RH module (4 ml stainless steel cell), were used in each trial according to the methodology below.
The response of the T. molitor larvae towards changes in humidity was studied by exposing the experimental animals to a flow of atmospheric air at a controlled rate and RH. To this end, the calorimeter was equipped with a 1131 RH control module (Thermometric), which regulated two computer-controlled mass flow valves (Bronkhorst, the Netherlands). During operation, dry atmospheric air is supplied from a tank to the mass flow valves, which generate two air streams of specific flow rates. One stream was saturated with water vapour in a series of two humidifying chambers in the RH 2250 calorimetric module (H in Fig. 1), while the other was led directly to the calorimetric cell. In this way, adjustment of the rates of the two air streams allowed control of the RH in the calorimetric cell A, which houses the larvae. This control may involve keeping a constant humidity or more complicated protocols of preprogrammed linear gradients in humidity or stepwise changes.
|
The parts of the 2250 calorimetric modules that are outside the TAM instrument as well as the Teflon® tubing that carries the gas flow were housed in a fanned box kept at 49±0.2°C (F in Fig. 1) on top of the TAM. This prevented any measurable adsorption of vapour in the auxiliary equipment.
Methodology
The experimental approach was based on the use of two serially connected
calorimetric modules, which were continuously purged with the stream of
atmospheric air from the mass flow valves
(Fig. 1). This set-up allowed
simultaneous, real-time measurement of the metabolic activity and the water
exchange of the larvae.
The air stream entered the first calorimetric cell (A in
Fig. 1) at a total air flow
rate Jair (volume/time) and a nominal RH,
RHsupply (in %). The thermal output (or heat flow) of cell A,
HFA, signifies the combined effect of the metabolic heat and the
thermal effects of water adsorbed or evaporated from the animal or the walls
of the calorimetric cell. Due to these adsorption/evaporation effects, the
actual RH in the calorimetric cell, RHcell,, which governs the
water exchange of the larvae, is usually different from RHsupply.
Subsequent to purging cell A, the air stream was led to cell B, which
contained 700 µl distilled water, and served to measure RHcell.
Thus, saturation of the purge gas with water vapour required a small
evaporation, and the associated endothermic heat flow of cell B,
HFB, directly reflected the humidity of the incoming air flow.
Thus, if the vapour is considered an ideal gas:
![]() | (1) |
Along the same lines, HFB can be used to quantify the exchange
of water between the animal and the gas stream. To do so, the adsorption
behaviour of cell A must be singled out in a control experiment where the
reference heat flows refHFA and
refHFB are measured under the same experimental
conditions, but with an empty cell in calorimeter A. Once the reference heat
flows are established, the difference HFB -
refHFB signifies whether the air stream is enriched or
depleted with respect to water during its passage over the larvae in cell A,
and the exchange of water, WH2O (mass/time),
can be written:
![]() | (2) |
When the water exchange WH2O has been
quantified, the calorimetric output HFA can be analysed with
respect to its constituent contributions. Hence the metabolic heat production
HFmetabol can be written:
![]() | (3) |
Mixing of gas in the volumes of calorimetric cells and the tubing introduces a delay in the detection (in cell B) of water absorbed by the animal (in cell A). This delay depends on the magnitude of the `dead-volume' and the flow rate Jair. Assuming fast equilibration of humidity gradients inside cell A, the delay follows an exponential time course and can readily be quantified. In this work, however, we did not apply any explicit time correction on WH2O. Rather, we established experimentally that the effects of this delay fell to undetectable levels within about 15 min. This is a satisfactory time resolution for the current purpose.
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
|
|
Fig. 3B shows an example of raw data from cell B, HFB (solid line). By analogy with Fig. 3A the graph in Fig. 3B is supplemented with refHFB (broken line) and RHsupply (dotted line). Inspection of the data shows that during the initial plateau at 60%RH, RHB was less negative than refHFB. This shows that the presence of the larva in cell A increased the humidity of the gas flow, or, in other words, that the animal was losing water. Conversely, towards the end of the trial, the observation that HFB<refHFB signifies water vapour absorption in the larva.
To facilitate quantitative interpretations, the functions RHcell, HFmetabol and WH2O were calculated from raw data like those in Fig. 3, and plotted against the experimental time as exemplified in Fig. 4A-C, which represents three larvae that had been pre-acclimated for 47-62 days without food. At the beginning of the calorimetric measurements the wet masses were, respectively, 19.79 mg, 45.95 mg and 33.08 mg. The curves in Fig. 4 show RHcell, (dotted lines), HFmetabol/Mw (broken lines) and WH2O/Mw (solid lines), where Mw is the wet mass of the animal at the beginning of the calorimetric measurement. Since HFmetabol and WH2O are expected to scale with the size of the experimental animal, these functions were normalized with respect to Mw before plotting the data in Fig. 4. The results in Fig. 4 and analogous data for trials not presented graphically showed several general features. Some of these are listed in Table 1, together with information of the pre-acclimation. It appears that the larvae consistently initiated WVA when RHcell reached 92.7±0.6%RH and that the absorption subsequently decreased RHcell to 88.6±0.5. Table 1 also lists the maximal absorption rate, which was 86±6 µg h-1 and independent of the body mass, and estimates of the average metabolic heat production during the initial (0-10 h) and intermediate (15-20 h) stages of the experiment.
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The Tenebrio molitor larvae investigated produced qualitatively
uniform results in the calorimetric trials, and several interesting trends can
be identified. Thus, a well-defined threshold value of 92.7±0.6%RH was
observed for the onset of WVA for animals exposed to a linear RH ramp
increasing at a slope of 3%RH per hour
(Table 1). Over the subsequent
5 h we observed a strong increase in WH2O
(Fig. 4), signifying the
absorption of water in the larva. The WH2O
function reached a steady (maximal) value of 86±6 µg h-1
about 10-15 h after the threshold RH had been passed. The WVA consistently
reduced RHcell to 88.6±0.5%
(Table 1). Interestingly, these
final values of WH2O and RHcell
showed no dependence on the size of the experimental animal. This suggests
that the WVA value observed here is limited by the magnitude of the RH
gradient or the amount of water furnished by the incoming moist air. Hence,
reduction of RH from 97% to 88.6% for Jair=45 ml
h-1 corresponds to a water uptake of 87 µg h-1. To
test this further we conducted two trials, in which Jair
was increased to 100 ml h-1
(Table 1). The results showed
slightly elevated maximal values of WH2O (90
and 112 µg h-1, respectively). The observation that the maximal
uptake rate does not scale with the supply of vapour as defined by
Jair at a fixed RH suggests that the values of
WH2O recorded here are indeed close to the
maximum capacity of the larvae, but a detailed analysis of this and its
dependence of the body size awaits further comparative studies. The
observation that T. molitor larvae may absorb water down to ambient
activities corresponding to approximately 88%RH is in accordance with previous
studies (Dunbar and Winston,
1975; Grimstone et al.,
1968
; Machin,
1975
,
1976
,
1978
;
Mellanby, 1932
; Noble-Nesbitt,
1973
,
1978
;
O'Donnell and Machin, 1991
;
Ramsay, 1964
). These latter
studies, however, did not report the existence of any RH threshold higher than
88%RH required to initiate WVA, although a threshold of 89.7%RH has been
discussed (Coutchié and Machin,
1984
). To test the existence of such a threshold more
specifically, we measured the water exchange in four larvae in trials where
the final value RHsupply was 90% (otherwise the experimental
parameters were equivalent to those used in the measurements illustrated in
Fig. 4). The data showed no
clear increase in WH2O during the 24 h exposure
to 90%RHsupply (corresponding to RHcell=86%), confirming
that the larvae investigated here require exposure to a threshold value
(>90%RH) to initiate WVA.
An interesting property observed for all trials was a conspicuous increase
in HFmetabol about 13 h into the experiment
(Fig. 4). At this point, the
base level of heat production typically doubled (from 5 to 10 J g-1
h-1) within a few hours. The increase in HFmetabol
consistently occurred 3 h prior to the initiation of WVA, and the heat
production stayed high during the initial stages of absorption. Later, as
WH2O approached a steady level, metabolic heat
production gradually decreased. The experiments with a maximal
RHsupply of 90% corresponding to a maximal RHcell of
about 86%, did not show WVA, and no increase in HFmetabol was
observed. Hence, we suggest that the increase in HFmetabol and the
initiation of WVA are correlated. The enhanced metabolic heat production sets
in at RHcell88%, i.e. the steady level observed during
prolonged WVA, and these observations raise intriguing questions regarding a
sensory regulation of WVA. For example, it seems to be of interest for future
work to investigate if the enhanced metabolism reflects preparation of the WVA
apparatus stimulated by a critical ambient humidity of about 88%. It could
tentatively be suggested that this preparation is redistribution of ions and
fluids within the cryptonephridial complex. It may also indicate a de
novo synthesis or rearrangement of strongly hygroscopic proteins (i.e.
thermal hysteresis proteins; Patterson and
Duman, 1978
) or other proteins earlier reported from Tenebrio
molitor (Kroeker and Walker,
1991
). The minimal (reversible) work associated with the transport
of water from RH=88% to the body of the larva is about 0.3 kJ mol-1
water. Using typical values of WH2O and body
mass (Table 1), this translates
into a heat flow of less than 0.5 J g-1 h-1, and
suggests that the enhanced metabolism directly required to sustain the maximal
WVA observed here is too small to be detected in the HFmetabol
function.
The HFmetabol traces showed a number of sharp peaks. This
behaviour has been studied in detail previously, and it was concluded that the
larger peaks (amplitude >20 µW) arise from wriggling movements, while
smaller peaks are due to abdominal pulsations and tracheal ventilation
(Harak et al., 1998;
Kuusik et al., 1994
).
Inspection of Fig. 4B, for
example, shows a clear tendency of decreased WVA during the occurrence of
large peaks in HFmetabol (wriggling) at the experimental times of
22 and 33 h. This is identified as the local minima in the
WH2O function, and the effect can readily be
quantified as the area of the `dips' in WH2O.
The examples in Fig. 4B suggest
that each of these two periods of wriggling, which last about 3 h, is coupled
to a cutback in WVA of about 60 µg water. This could be either a result of
a less efficient WVA in moving larvae or (more likely) water loss through a
separate process such as enhanced respiration in the active animals. A
qualitatively similar observation was made for the smaller peaks (
10 µW
due to pulsation/ventilation), and analysis of the `dips' in the
WH2O function suggests a concomitant water loss
of 10-15 µg over a period of about 30 min. Systematic calorimetric studies
of interrelationships between respiratory activity and water loss are
currently in progress.
In conclusion, we have found that calorimetry is an effective tool for real-time studies of WVA in small invertebrates. The current results show that upon exposure to a threshold value of 92-93%RH, T. molitor absorbs water at a rate of about 90 µg h-1. During the absorption, the humidity of the experimental chamber was reduced to 88%RH despite continuous perfusion with air that was practically water saturated. The onset of WVA was preceded by a pronounced increase in the metabolic heat, and this parameter gradually decreased to the pre-WVA level over the following 24 h of water absorption. This suggests a sensatory and active control of WVA.
List of abbreviations
![]() |
Acknowledgments |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Audsley, N., Coast, G. M. and Schooley, D. A.
(1993). The effects of Manduca sexta diuretic hormone on
fluid transport by the Malpighian tubules and cryptonephric complex of
Manduca sexta. J. Exp. Biol.
178,231
-243.
Bäckman, P. and Wadsö, I. (1991). Cell growth experiments using a microcalorimetric vessel equipped with oxygen and pH electrodes. J. Biochem. Biophys. Meth. 23,283 -293.[CrossRef][Medline]
Beament, J. W. L. (1959). The waterproofing mechanism of arthropods. J. Exp. Biol. 36,391 -422.
Buxton, P. A. (1930). Evaporation from the meal-worm (Tenebrio: Coleoptera) and atmospheric humidity. Proc. R. Soc. Lond. B 106,560 -577.
Clarke, E. C. W. and Glew, D. N. (1985). Evaluation of the thermodynamic functions for aqueous sodium chloride from equilibrium and calorimetric measurements below 154°C. J. Phys. Chem. Ref. Data 14,489 -610.
Coutchié, P. A. and Machin, J. (1984). Allometry of water vapor absorption in two species of Tenebrionid beetle larvae. Am. J. Physiol. 247,230 -236.
Dauncey, M. J. (1991). Whole-body calorimetry in man and animals. Thermochim. Acta 193, 1-40.[CrossRef]
Dunbar, B. S. and Winston, P. W. (1975). The site of active uptake of atmospheric water in larvae of Tenebrio molitor.J. Insect Physiol. 21,495 -500.[CrossRef]
Edney, E. B. (1971). Some aspects of water balance in Tenebrionid beetles and a Thysanuran from the Namib desert of southern Africa. Physiol. Zool. 44, 61-76.
Gibbs, A. G., Louie, A. K. and Ayala, J. A.
(1998). Effects of temperature on cuticular lipids and water
balance in a desert Drosophila thermal acclimation beneficial?
J. Exp. Biol. 201,71
-80.
Grimstone, A. V., Mullinger, A. M. and Ramsay, J. A. (1968). Further studies on the rectal complex of the mealworm Tenebrio molitor, L. (Coleoptera, Tenebrionidae). Phil. Trans. R. Soc. Lond. A 253,334 -382.
Guan, Y. H., Lloyd, P. C. and Kemp, R. B. (1999). A calorimetric flow vessel optimised for measuring the metabolic activity of animal cells. Thermochim. Acta 332,211 -220.[CrossRef]
Hadley, N. F. (1994). Water Relation of Terrestrial Arthropods. San Diego: Academic Press, Inc.
Harak, M., Kuusik, A., Hiiesaar, K., Metspalu, L., Luik, A. and Tartees, U. (1998). Calorimetric investigations on physiological stress in Tenebrio molitor (Coleoptera, Tenebrionidae) pupae. Thermochim. Acta 309, 57-61.[CrossRef]
Harak, M., Lambrecht, I. and Kuusik, A. (1996). Metabolic cost of ventilating movements in pupae of Tenebrio molitor and Galleria mellonella studied by direct calorimetry. Thermochim. Acta 276,41 -47.[CrossRef]
Harak, M., Lambrecht, I., Kuusik, A., Hiiesaar, K., Metspalu, L. and Tartees, U. (1999). Calorimetric investigations of insect metabolism and development under the influence of a toxic plant extract. Thermochim. Acta 333,39 -48.[CrossRef]
Johansson, P. and Wadsö, I. (1999). Towards more specific information from isothermal microcalorimetric measurements on living systems. J. Therm. Anal. Cal. 57,275 -281.[CrossRef]
Kroeker, E. M. and Walker, V. K. (1991). Dsp28: A desiccation stress protein in Tenebrio molitor haemolymph. Arch. Insect Biochem. Physiol. 17,169 -182.
Kuusik, A., Tartees, U., Harak, M., Hiiesaar, K. and Metspalu, L. (1994). Developmental changes during metamorphosis in Tenebrio molitor (Coleoptera: Tenebrionidae) studied by calorimetric thermography. Eur. J. Entomol. 91,297 -305.
Lambrecht, I. (1998). Monitoring metabolic activities of small animals by means of microcalorimetry. Pure Appl. Chem. 70,695 -700.
Lehto, V.-P. and Laine, E. (2000). Simultaneous determination of the heat and the quantity of vapor sorption using a novel microcalorimetric method. Pharm. Res. 17,701 -706.[CrossRef][Medline]
Lindstrom, P. J. and Mallard, W. G. (2003). Nist standard reference database number 69. In NIST Chemistry Web Book (ed. P. J. Lindstrom and W. G. Mallard), http://webbook.nist.gov. Gaithersburg, MD: National Institute of Standards and Technology.
Machin, J. (1975). Water balance in Tenebrio molitor, L. larvae; the effect of atmospheric water adsorption. J. Comp. Physiol. B 101,121 -132.
Machin, J. (1976). Passive exchanges during water vapour absorption in mealworms (Tenebrio molitor): A new approach to studying the phenomenon. J. Exp. Biol. 65,603 -615.[Abstract]
Machin, J. (1978). Water vapour uptake by Tenebrio: A new approach to studying the phenomenon. In Comparative Physiology - Water, Ions and Fluid Mechanism (ed. L. Bolis, K. Schmidt-Nielsen and S. H. P. Maddrell), pp. 67-77. Cambridge: Cambridge University Press.
Machin, J. and O'Donnell, M. J. (1991). Rectal complex ion activities and electrochemical gradients in larvae of the desert beetle, Onymacris: Comparisons with Tenebrio. J. Insect Physiol. 37,829 -838.[CrossRef]
Markova, N. and Wadsö, L. (1999). A microcalorimetric study of water vapor sorption on morphine sulphate. J. Therm. Anal. Cal. 57,133 -137.[CrossRef]
Mellanby, K. (1932). The effect of atmospheric humidity on the metabolism of the fasting mealworm (Tenebrio molitor L., Coleoptera). Proc. R. Soc. Lond. B 111,376 -390.
Noble-Nesbitt, J. (1970). Structural aspects of penetration through insect cuticles. Pest. Sci. 1, 204-208.
Noble-Nesbitt, J. (1973). Rectal uptake of water in insects. In Comparative Physiology (ed. L. Bolis, K. Schmidt-Nielsen and S. H. P. Maddrell), pp.333 -351. New York: Elsevier.
Noble-Nesbitt, J. (1978). Absorption of water vapour by Thermobia domestica and other insects. In Comparative Physiology - Water, Ions and Fluid Mechanics (ed. K. Schmidt-Nielsen, L. Bolis and S. H. P. Maddrell), pp. 53-66. Cambridge: Cambridge University Press.
O'Donnell, M. and Machin, J. (1991). Ion activities and electrochemical gradients in the mealworm rectal complex. J. Exp. Biol. 155,375 -402.
Patterson, J. L. and Duman, J. G. (1978). The role of the thermal hysteresis factor in Tenebrio molitor larvae. J. Exp. Biol. 74,37 -45.
Pelletier, Y. (1995). Effects of temperature and relative humidity on water loss by the Colorado potato beetle, Leptinotarsa decemlineata (Say). J. Insect. Physiol. 41,235 -239.[CrossRef]
Ramløv, H. and Lee, R. E. (2000).
Extreme resistance to desiccation in overwintering larvae of the gall fly
Eurosta solidaginis (Diptera, Tephritidae). J. Exp.
Biol. 203,783
-789.
Ramsay, J. A. (1964). The rectal complex of the mealworm Tenebrio molitor, L (Coleoptera, Tenebrionidae). Phil. Trans. R. Soc. Lond. A 248,280 -313.
Schaatschmidt, B., Matuschka, F.-R. and Lambrecht, I. (1995). Direct and indirect calorimetric investigations on some snakes. Thermochim. Acta 251,261 -269.[CrossRef]
Schmolz, E., Drutschmann, S., Schricker, B. and Lambrecht, I. (1999). Calorimetric measurements of energy contents and heat production rates during development of the wax moth Galleria mellonella. Thermochim. Acta 337, 83-88.[CrossRef]
Schmolz, E., Hoffmeister, D. and Lambrecht, I. (2002). Calorimetric investigations on metabolic rates and thermoregulation of sleeping honeybees (Apis mellifera carnica). Thermochim. Acta 382,221 -227.[CrossRef]
Schmolz, E. and Lambrecht, I. (2000). Calorimetric investigations on activity states and development of homometabolous insects. Thermochim. Acta 349, 61-68.[CrossRef]
Suurkuusk, J. and Wadsö, I. (1982). A multichannel microcalorometry system. Chem. Scr. 201,155 -163.
Wadsö, I. and Wadsö, L. (1996). A new method for determination of vapour sorption isotherms using a twin double microcalorimeter. Thermochim. Acta 271,179 -187.[CrossRef]
Wadsö, I. and Wadsö, L. (1997). A second generation twin double microcalorimeter: Measurements of sorption isotherms, heats of sorption and sorption kinetics. J. Thermal Anal. 49,1045 -1052.
Weast, R. C. (1986). CRC Handbook of Chemistry and Physics (ed. M. J. Astle and W. H. Beyer). Boca Raton, Florida: CRC Press, Inc.
Wharton, G. W. and Richards, G. A. (1978). Water vapor exchange kinetics in insects and acarines. Ann. Rev. Entomol. 23,309 -328.[CrossRef]
Williams, A. E., Rose, M. R. and Bradley, T. J.
(1998). Using laboratory selection for desiccation resistance to
examine the relationship between respiratory pattern and water loss in
insects. J. Exp. Biol.
201,2945
-2952.