Thermoregulation in moulting and feeding Danaus plexippus L. (Lepidoptera: Nymphalidae) caterpillars

Body temperature in insects is affected by interactions between environmental variables, behavioural choices and the physiological state of the animal. Insect larvae display a number of tactics for thermoregulation which allow their body temperatures to deviate several degrees from ambient. Thermoregulatory adaptations can reduce generation time and allow higher population growth rates. However, few investigations have examined thermoregulation of moulting larvae. This study measured whether moulting Monarch butterfly (Danaus plexippus) larvae thermoregulate, and, if so, whether they thermoregulate similarly to feeding larvae. Body temperatures of moulting and feeding larvae were compared to their microhabitat temperatures. In three of four environments, feeding larvae were able to thermoregulate in such a way that their body temperature was higher than ambient at low ambient temperature, and lower than ambient at higher ambient temperature. However, moulting larvae appear not to thermoregulate because their body temperature did not differ from ambient in three of four environments. These results pose the question of whether larvae are behaviourally and/or physiologically constrained from thermoregulating during the moulting process. Additional studies are needed to address such questions and would help to elucidate the impact of thermoregulation of moulting larvae on the ecology and evolution of insects.