Calorimetric investigations on special insects

Early calorimetric investigations were performed on pupae of the wax moth Galleria mellonella by means of a differential adiabatic setup [92]. Galleria represents an important pest for weak honeybee colonies where it feeds on wax, honey, pollen and other organic material. Individual pupae were kept in small Dewar flasks of 5 cm for measurements of 10 to 60 min, which were repeated in regular intervals through the whole pupal metamorphosis of about 7 days. The calorimetric experiments alternated with manometry (indirect calorimetry) to evaluate the RQ and to find hints about the type of metabolism. Heat dissipation was monitored by electrical heating of the reference flask to keep the temperature difference between both Dewars close to zero. In this way composite curves for male and female moths and both direct and indirect calorimetry were established. 

Moreover, the manometric data were transformed to heat dissipation and compared with the direct values. The considerable differences between both might be due to evaporation and to a wrong assumption that only fat and no protein was metabolized during metamorphosis. Sex differences as well as an U-shaped course of energy turnover during pupal metamorphosis occured, observed also by other authors. 

Custom-made simple thermocouple calorimeters of 0.25 mL active volume and a sensitivity of 20 pV/mW were applied to study the growth regulating and toxic effects of Ledum palustre extracts on the growth of pupae of T. molitor [103]. They exhibited the U-shaped course of mass-specific heat production rate (max. 2.8 mW/g, min. 1.2 mW/g) as described also by other authors (e.g. [88,92]). Superimposed on the slope were longer-lasting clear endothermic structures during 

Microcalorimetric experiments were used to analyse the well-known drastic temperature increase in laboratory cultures of Galleria mellonella during larval development. The authors showed that the temperature rise was due to an approximately threefold increase in mass specific heat production rates from about 50 mW/g for the larval stage L3 to about 140 mW/g for L4 and L5 (followed by a drop to 75 mW/g for L6) [104]. The observed aggregation of larvae inside silken tubes was thus unlikely to be responsible for the temperature jump from 32 to 40 °C during stages L4 and L5 vidiich are typical for G. mellonella in laboratory cultures. 

With the same calorimeter, B. germanica was investigated for its answer to anaesthesia with CO2. The basal metabolic rate amounted to about 1.3 mW/g at 25 °C. Introduction of CO2 into the gas flow induced an irritation of the insect and a subsequent cessation of heat production. A re-aeration 2 h later led to an enormous increase of heat production up to more than 9 mW/g and later 6 mW/g which returned to the initial level of basal metabolism only after a few days [107]. 

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