Spatiotemporal Variability and Foraging Behavior of Bee Visitors to a Rare Long-lived Perennial Iteroparous Forb, Silene spaldingii (Charyophyllaceae)

Authors: HATTEN, TIMOTHY - Invertebrate Ecology Inc; Griswold, Terry; GIBBS, JASON - University Of Manitoba

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2024
Publication Date: 10/21/2024
Citation: Hatten, T.D., Griswold, T.L., Gibbs, J. 2024. Spatiotemporal Variability and Foraging Behavior of Bee Visitors to a Rare Long-lived Perennial Iteroparous Forb, Silene spaldingii (Charyophyllaceae). Scientific Reports. https://doi.org/10.1038/s41598-024-75836-w.
DOI: https://doi.org/10.1038/s41598-024-75836-w

Interpretive Summary: Spalding’s Catchfly is a rare flowering plant found in the open native grasslands of the Inland Pacific Northwest in southeastern Washington and adjacent parts of Idaho and Oregon. Because it is rare, there is concern about it producing enough seeds to maintain the plant. Bumble bees are thought to be the pollinators of Spalding’s Catchfly but their abundance can vary a lot and at least one of the bumble bees is declining. This study looked at whether there were additional bees that supplement the pollination by bumble bees. Are there other bees that do or can contribute to reproduction? This study found that there are many kinds of bees and lots of individual bees where Spalding’s Catchfly grows. But of the 81 bee species less than 10% visited Spalding’s Catchfly. One of these bees, a sweat bee (Halictus tripartitus), is an abundant, effective pollinator of Spalding’s Catchfly. Another sweat bee had never before been found in North America. This study will assist in conserving a rare plant.

Technical Abstract: Silene spaldingii S Watson is a rare long-lived forb (Charyophyllaceae) found primarily in open native grasslands of the Inland Pacific Northwest and is putatively pollinated by one key bumble bee pollinator, Bombus fervidus (Fabricius). However, populations of bumble bees and their visitation patterns can vary dramatically, and some species are in decline including B. fervidus. Understanding the role of co-pollinators such as sweat bees (Halictidae) could be crucial as the plight of rare plants and pollinators intensifies. We collected data across three seasons (2015-2017) on the Bombus-S. spaldingii pollination system, focusing on three Key Conservation Areas (KCAs) in the Channeled Scablands of eastern Washington. Bee visitors to S. spladingii were monitored and the pool-of-pollinators was surveyed with blue vane traps. Nine species of bee were observed foraging on the plant, while 2211 bees comprised of five families, 22 genera and 81 taxa were captured in Blue vane traps, meaning less than 10% of species in the pollinator pool visited S. spladingii. Halictus tripartitus Cockerell, a sweat bee, was a common visitor to the plant, but this was the first record of visitation for several other species, including L. buccale (Pérez) which has never before been recorded in the Americas. All these bees appear to vector S. spladingii pollen, indicating they are co-pollinators of the plant. Weather and patch characteristics affected visitation patterns and the pool-of-pollinators. We conclude that sweat bees are co-pollinators.