LB 33-276 - Native plants and native cultivars: Understanding pollinator preference for native plants and their cultivated counterparts in the Pacific Northwest

Native cultivars present a paradox for ecologically-minded gardeners: growing interest in native plants is largely related to their purported benefits to pollinators, yet many native plants found at nurseries may be significantly altered, compared to wild genotypes. The goals of our research are to identify potential differences in pollinator preference for wild type natives or cultivars, and to understand what floral traits plant breeding impacts. Over three field seasons (2020-2022), we conducted 5-minute observations of insect pollinators to 5 species of Pacific Northwest native plants and one to three associated cultivars. Native plants included three perennials: Douglas’ Aster (Symphyotrichum subspicatum), Yarrow (Achillea millefolium), Western-red Columbine (Aquilegia formosa), and two annuals: California Poppy (Eschscholzia californica) and Farewell-to-spring (Clarkia amoena). Pollinator counts were conducted before, during, and after peak bloom (25-100% bloom coverage) on 5 1x1m2 replicates of each individual plant type. Pollinators were identified to the lowest taxonomic level possible (e.g., species for honey bees, color groups for bumblebees, family level for flower flies, etc).We hypothesized that pollinator preference for native status (natives or cultivars) would vary by plant species group. We used negative binomial and zero-inflated negative binomial mixed effects models to examine the relationship between pollinator preference, plant type, and year, with plot number as a random effect. We calculated model estimates for each of the fixed effects using Estimated Marginal Means, and employed a Bonferroni-adjusted alpha level to conduct pre-planned comparisons between natives and cultivars for different pollinator groups. Pollinator groups were as follows: all pollinators (all bees, butterflies, and flower flies), all bees (butterflies and flower flies removed), wild bees (non-native Apis mellifera removed), bumblebees (Bombus spp.), long-horned bees (Eucerini), leafcutter bees (Megachilidae), flower flies (Syrphidae & Bombyliidae), and butterflies (Papilionoidea).In most native-cultivar comparisons, pollinator taxa exhibited no significant preference for either plant type. In significant comparisons, native plants were preferred 82% of the time, with long-horned bees, flower flies, and butterflies preferring native plants 100% of the time. Douglas’ Aster was the only species where cultivar preference occurred, for all pollinators, all bees, and bumble bees. Detailed measurements of plant traits may help identify which ornamental characteristics influence pollinator visitation to native plants and native cultivars, which is the focus of our current work. Though there is no trend across all plant and pollinator groups, we recommend wild-type native plants for conservation and pollinator gardens, to ensure specialist pollinators can meet their nutritional requirements.