Reproductive ecology and bee associates of Packard’s milkvetch (Astragalus packardiae), a rare plant endemic to southwestern Idaho

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Conservation of rare plants is dependent on identifying mechanisms that limit their population or persistence. Successful pollination of flowers is one life history trait that is often limiting in plants occurring in fragmented landscapes. We studied pollinator associates and seed production in Astragalus packardiae (= A. cusickii var. packardiae, Packard’s milkvetch), a narrow endemic that is imperiled as a result of nonnative annual grasses, increased wildfire, recreational off-highway vehicle use, and livestock use. We used pollinator exclusion bags to examine the breeding system of Packard’s milkvetch. We collected and videotaped floral visitors to determine the makeup of the associates and the visitation rate to flowers. Our study demonstrates that Packard’s milkvetch is highly dependent on pollinators for reproductive success. Plants that were excluded from pollinator visitation produced a mean of 0.05 seeds/fruit (SD = 0.21), while plants open to pollinator visitation produced 2.44 seeds/fruit (SD = 1.03) (Wilcoxon signed-rank test: n = 23, P < 0.001). We collected a total of 203 floral visitors of A. packardiae. The order Hymenoptera (bees and wasps) made up 86% of the visitors, of which wasps were merely 1% of the collected insects. Lepidoptera (butterflies), Coleoptera (beetles), and Diptera (flies) accounted for the remaining 7%, 4.4%, and 2.5% of visitors, respectively. The bee associates were markedly composed of Osmia bee species. Visitation rate for Packard’s milkvetch was 3.8 visits/flower per hour, which is within the range of other studied Astragalus species. Because seed production in Packard’s milkvetch is highly dependent on native bees, future conservation of Packard’s milkvetch is reliant on the conservation of native bee habitat.

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Reference Code: A23FUL01IDUS <br>

Full Citation: Fulkerson, Justin R. and Kinter, C. Lynn (2023) "Reproductive ecology and bee associates of Packard’s milkvetch (Astragalus packardiae), a rare plant endemic to southwestern Idaho," Western North American Naturalist: Vol. 83: No. 2, Article 9. Available at: https://scholarsarchive.byu.edu/wnan/vol83/iss2/9. <br>

Location: ELECTRONIC FILE - BOTANY: PLANT SPECIES: Astragalus packardiae <br>

Keywords: Astragalus packardiae, Astragalus cusickii var. packardiae, Packard’s milkvetch, pollinators, rare plant conservation, Osmia <br>