Pollen column, and a wax canopy, in a first nest description of Bombus (Cullumanobombus) morrisoni (Apidae)

Authors: Koch, Jonathan; CANE, JAMES - Retired ARS Employee

Submitted to: Apidologie
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2022
Publication Date: 6/21/2022
Citation: Koch, J., Cane, J.H. 2022. Pollen column, and a wax canopy, in a first nest description of Bombus (Cullumanobombus) morrisoni (Apidae). Apidologie. 53. Article 31. https://doi.org/10.1007/s13592-022-00943-4.
DOI: https://doi.org/10.1007/s13592-022-00943-4

Interpretive Summary: Bumble bee diversity reflects successful colony stages in the overall bumble bee life cycle. However, their nesting biologies are generally far less studied than their foraging ecologies, particularly for wild nests in the field. In this study, we describe the first reported nest of Bombus morrisoni, a species with an extensive range in the arid Intermountain of the Nearctic. The mature, naturally terminated nest consisted of 424 nest cells (cocoons), with 328 cells belonging to non-gynes and 94 gyne cells. Of notable importance, we document the presence, dimensions, orientation, and significance of pollen pillars and wax covering. The contribution of our study adds to the phylogenetic diversity of wild bee nest studies, which may increase the capacity to test hypotheses associated with larval feeding strategies and environmental orientation. Our study also raises unanticipated questions, such as the purpose of pollen addition to wax canopies, and why this large B. morrisoni nest expired despite large pollen and nectar surpluses and a bevy of worker and gyne pupae ready to emerge.

Technical Abstract: Bumble bee diversity reflects successful colony stages in the overall bumble bee life cycle. However, their nesting biologies are generally far less studied than their foraging ecologies, particularly for wild nests in the field. In this study, we describe the first reported nest of Bombus morrisoni, a species with an extensive range in the arid Intermountain of the Nearctic. The mature, naturally terminated nest consisted of 424 nest cells (cocoons), with 328 cells belonging to non-gynes and 94 gyne cells. Furthermore 25% of the cells contained gyne and non-gyne pupae in sealed cocoons. The nest also had two kinds of understudied structures associated with bumble bee nests: pollen columns and a wax canopy. We found five pollen columns rising amid the cocoons. The five vertical columns were built from about 1200 stacked corbicular pollen loads. A 0.3 mm thick wax canopy spanned over the entire nest. An estimated 40 million pollen grains were incorporated into the 19 g wax canopy, demonstrating that some bumblebee species devote substantial pollen to this non-dietary-purpose. Insights into their nesting needs and realized reproductive output gained through our detailed, quantified nest description of B. morrisoni contributes to much needed comparative accounts of bumble bee nesting biology, with implications for management and conservation decisions. Our study also raises unanticipated questions, such as the purpose of pollen addition to wax canopies, and why this large B. morrisoni nest expired despite large pollen and nectar surpluses and a bevy of worker and gyne pupae ready to emerge.