5.3. Operative temperature

In field investigations of honey bee thermoregulation, operative temperature (Te) provides an integrated measure of the action of several environmental factors on honey bee thermoregulation (Fig. 8). Te is the body temperature of dead honey bees exposed to the same environmental conditions as the living bees under investigation. It allows separating the endogenous part of thermoregulation (endothermy) from the effect of environmental parameters on body temperature (Kovac et al., 2010). These environmental parameters are ambient air temperature, radiative loss and gain of heat, thermal convection and external air convection (wind), and evaporative heat loss, mainly through the cuticle. In such experiments, dead honey bees are used as thermosensors (Fig. 8). Te has been determined by using both dried or fresh carcasses. However, using fresh carcasses is recommended, because the use of dried bees strongly reduces honey bee heat capacity (because of their smaller mass), and this way considerably changes the reaction of the Te-thermometer to environmental factors. For a detailed discussion of this topic see Materials and Methods in Kovac et al. (2010).

Fig. 8. Operative temperature (Te) measurement in honey bees. Te is the body temperature of dead bees exposed to the same environmental conditions as the living individuals under investigation. It can be measured either thermographically as surface temperature (a) or by an implanted thermocouple as core temperature (b). Graph by Anton Stabentheiner.

Figure 8