Likelihood of same diapause fate for nest-adjacent siblings of alfalfa leafcutting bees (Megachile rotundata, Hymenoptera: Megachilidae)

Authors: McCabe, Lindsie; Pitts Singer, Theresa

Submitted to: Current Research in Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2025
Publication Date: 9/4/2025
Citation: Mccabe, L.M., Pitts Singer, T. 2025. Likelihood of same diapause fate for nest-adjacent siblings of alfalfa leafcutting bees (Megachile rotundata, Hymenoptera: Megachilidae). Current Research in Insect Science. Volume 56, article number 78, (2025). https://doi.org/10.1007/s13592-025-01209-5.
DOI: https://doi.org/10.1007/s13592-025-01209-5

Interpretive Summary: The alfalfa leafcutter bee, Megachile rotundata, is a critical pollinator for commercial alfalfa seed production. These solitary bees exhibit facilitative diapause traits. Diapause, a state of suspended development, can be triggered by various environmental factors, including photoperiod and maternal condition. While the precise mechanisms underlying this developmental decision remain elusive, it is evident that sibling bees within a nest often share a common diapause fate. We investigated this phenomenon by examining adjacent cells in nests collected from alfalfa fields. They found a strong correlation between the diapause status of neighboring siblings, particularly during specific time periods. While the exact reasons for this synchronicity are still under investigation, it suggests that genetic or environmental cues may play a significant role in coordinating the developmental trajectories of these solitary bees.

Technical Abstract: Megachile rotundata, the alfalfa leafcutting bee, is an intensely managed solitary bee used primarily for the commercial pollination of alfalfa seed. They have a unique life-cycle where each bee will either experience a yearly life cycle (diapausing individuals) or a shortened life cycle, where they complete pupation to adult during the same summer their egg was laid (non-diapausing individuals). The mechanism for this occurrence is still not greatly understood, although a maternal effect and photoperiod has been hypothesized. We sought to understand how likely siblings in the same nest would go through diapause or not. We used data gathered from two alfalfa sees farms in 2022. Cells were monitored over time to assess diapausing and non-diapausing individuals. We found that overall, 91% of siblings has the same diapausing fate. However, time of year played a role how likely it was for siblings to have the same fate. During the summer solstices siblings were only 76% likely to have the same diapausing fate, where several weeks before or after this time period siblings were close to 100% the same.