Entomological Society of America
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Thermoregulatory responses to diapause induction cues vary with caste and life stage in bumblebees
New bumblebee queens emerge in late summer and early autumn and are the only members of their natal colonies to survive through winter. Thus, winter survival of new bumblebee queens through diapause is crucial to the survival of the species, but diapause induction cues for bumblebees are not well known. Both photoperiod and temperature cues affect insect diapause, but temperature may be particularly important to bumblebees because fall queens only briefly experience photoperiod cues during a short 2-3 week period prior to diapause and they can alter the timing of diapause entry in response to resource availability. As bumblebees are heterotherms, thermoregulation provides a means to monitor induction into diapause while they transition from a metabolically active to a metabolically suppressed state. We used thermal imaging to monitor body temperatures of Bombus impatiens workers, new queens, carbon dioxide treated queens which are physiologically akin to spring queens, and late stage foundress queens (those with large colonies) as they cooled from 22 to 4 C. Workers showed a preference to stay warm as long as possible, whereas new queens and spring queens gradually cooled with cooling temperatures. Body temperatures of late-stage foundress queens tracked environmental temperatures. We did not identify a thermoregulatory pattern unique to new queens, the diapausing life-stage, and reproductive investment of later queen life stages did not inhibit the cooling response. Instead, the results suggest that queens retain an ability to adapt to cold past the new queen life-stage and may also lose their heterothermic ability with age.
Presenting Author: Megan Dillon
Co-Authors: Michael E. Dillon, PhD