Flexibility in the critical period of nutrient sequestration in bumble bee queens

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Yadira Romero Diaz, Entomology, UC Riverside, Riverside, CA, S. Hollis Woodard, Claudineia P. Costa and Kristal Watrous, Entomology, University of California Riverside, Riverside, CA

Background/Question/Methods
The solitary life stage of the bumble bee queen is understudied. Young queens, referred to as gynes, start their solitary life when they leave their natal nest. Queens hibernate and undergo diapause, a period of metabolic arrest. Gynes need enough nutrients to survive overwintering and the amount of nutrients they store depends in part on the type of floral resources available before diapause. We examined flexibility in the time period before diapause in the bumble bee Bombus impatiens. Specifically, we explored whether queens can adequately store nutrients after surviving periods of short-term deprivation of either artificial nectar or pollen.
We took young queens, measured their weight, then fed them one of nine diet treatments. Treatments consisted of nectar starvation (NS) or pollen starvation (PS) for durations of three, six, nine or twelve days. Queens deprived of either food for three, six, or nine days were then subsequently switched to the control diet for the remainder of the twelve days. Our control group had access to pollen and nectar for twelve days. Weights were recorded every other day and at the end of the twelve-day period. Nutrient levels (lipid and glycogen) were also quantified at the end of the experiment.

Results/Conclusions
The majority of queens survived the experiment. Queens starved of nectar for any duration had no difference in lipid concentrations when compared to the control. Glycogen concentrations were also not impacted by temporary starvation. Queens that were nectar starved for 3-6 days did not gain weight during this period, but were ultimately able to recuperate this weight. Queens starved for a longer period did not survive. Queens temporarily deprived of pollen for any duration were also able to recuperate with respect to weight and nutrient levels. Overall, this work shows that queens are able to recover after being temporarily nectar- or pollen-starved during the pre-diapause period.
Studying the solitary life stages of bumble bee queens is critical to understand population level patterns. It is important to recognize the ways in which queens are able to recover after stressful early adulthood experiences, such as limited access to food. Our study shows that there is some resiliency on the part of queens, but this should be balanced with the known deleterious effects of nutritional stress in bumble bees.