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Co-dependency between a specialist Andrena bee and its death camas host, Toxicoscordion paniculatum


Among associations of plants and their pollinating bees, mutually specialized pairings are rare. Typically, either pollen specialist (oligolectic) bees are joined by polylectic bees in a flowering species’ pollinator guild, or specialized flowers are pollinated by one or more polylectic bees. The bee Andrena astragali is a narrow oligolege, collecting pollen solely from two nearly identical species of death camas (Toxicoscordion, formerly Zigadenus). Neurotoxic alkaloids of these plants are implicated in sheep and honey bee poisoning. In this study, T. paniculatum, T. venenosum and co-flowering forbs were sampled for bees at 15 sites along a 900-km-long east–west transect across the northern Great Basin plus an altitudinal gradient in northern Utah’s Bear River Range. Only A. astragali bees were regularly seen visiting flowering panicles of these Toxicoscordion. In turn, this bee was never among the 170 bee species caught at 17 species of other prevalent co-occurring wildflowers in the same five state region (38,000 plants surveyed). Our field pollination experiments show that T. paniculatum is primarily an outcrosser dependent on pollinator visitation for most capsule and seed set. Thus, both A. astragali and two sister species of Toxicoscordion are narrowly specialized and co-dependent on each other for reproduction, illustrating a rare case of obligate mutual specialization in bee–plant interactions.

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Carole Scofield and others assisted with the exacting field pollinations and seed processing. Harold Ikerd at PIRU searched the museum specimen database. Byron Love was integral to bee collections at wildflowers. Dr. Vincent Tepedino provided a detailed, constructive review.

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Correspondence to James H. Cane.

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Plate 1. Six images showing: 1) Sagebrush-steppe landscape, Independence Mountains in background (photos 1-3 Elko Co., Nevada, USA). 2) two years after fire, blackened shrub skeletons and flowering Achillea, Allium, Crepis, Lupinus and T. paniculatum. 3) Flowering T. paniculatum showing a paniculate inflorescence. 4) Flowering T. paniculatum, Logan Utah, USA. 5) Flowering T. venenosum panicle, Lander, Wyoming USA. 6) Female A. astragali collecting yellow pollen from T. paniculatum panicle (JPG 3658 KB)

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Cane, J.H. Co-dependency between a specialist Andrena bee and its death camas host, Toxicoscordion paniculatum. Arthropod-Plant Interactions 12, 657–662 (2018).

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  • Apiformes
  • Breeding biology
  • Monolecty
  • Pollination
  • Oligolecty
  • Melanthiaceae
  • Zigadenus