Mattea Allert, 2013

University of Wisconsin Platteville

The Effect of Parasitism on Thermoregulation in Bumblebees

Bumblebees pollinate many wildflowers and economically important crops. They are known to forage under a wider range of temperatures than most other insect pollinators, due in great part to their well-developed thermoregulatory system. Despite this ability, some bumblebees too cold to fly are frequently found resting on plants just before sunset or during cooler than usual summer days, while other bumblebees are actively foraging. Because these torpid bees are disproportionately parasitized by fly parasites (Conopidae), previous researchers have suggested that parasites impair thermoregulation in bumblebees, rendering them incapable of flight during cool conditions. We tested this by chilling bumblebees in a refrigerator for 15 hours and then timing four stages of warm-up: twitching, standing, panic, and flying in a confined space. We found that parasitized bumblebees took significantly more time to stand after chilling than non-parasitized bumblebees, and exhibited a marginally non-significant trend of taking more time to twitch. There was no significant difference among parasitized and non-parasitized bumblebees in panicking or flying, both of which were less commonly exhibited behaviors in the confines of the experimental set-up. Within parasitized bumblebees, size of parasite did not influence the time to any behavior. This work shows that parasites can impede some aspects of thermoregulation in bumblebees and may contribute through this mechanism to the reduced activity seen among parasitized bees in the field. Reduced activity has consequences both for the competitive ability of the bee in bringing back resources to its colony and for the bee's ability to carry out pollination under variable weather conditions.


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