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Pollinator Syndromes

Pollinator syndromes are the characteristics or traits of a flower that appeal to a particular pollinator. These traits often help pollinators locate flowers and the resources (e.g. pollen or nectar) that the flowers have to offer.

Syndromes include bloom color, the presence of nectar guides, scents, nectar, pollen, and flower shapes. We can use these traits to predict what pollinators might be attracted to certain flowers or we can use these tools to guide us to pick the right plant for the right pollinator!

Bees, for example, are most attracted to flowers that have white, yellow, blue, or ultra-violet blooms.

Male long-horned bee on a white bindweed flower

Orange bumblebee (*Bombus sp*.) on a sunflower

Pollinator Syndromes for Bees & Butterflies

Table adapted from the North American Pollinator Protection Campaign

Trait	Bees	Butterflies
Color	White, yellow, blue, UV	Red, purple
Nectar Guides	Present	Present
Odor	Fresh, mild, pleasant	Faint but fresh
Nectar	Usually present	Ample, deeply hidden
Pollen	Limited; often sticky or scented	Limited
Flower Shape	Shallow; with landing platform, tubular	Narrow tube with long spur; wide landing pad

What are nectar guides?

Nectar guides are visual cues, such as patterns or darker colors in the center of a flower, that lead pollinators to nectar or pollen. These cues are beneficial to plants and their pollinators because they can reduce flower handling time, which allows bees to visit more flowers and transfer more pollen in a shorter amount of time.

Northern Blue Flag Iris (Iris versicolor).

The petals (yellow arrow) and sepals (red arrow) both have dark purple nectar guides. The yellow portion of the sepals may also be a nectar guide!

Image courtesy of Mike LeValley and the Isabella Conservation District Environmental Education Program

While the iris’s nectar guides are visible to humans and their pollinators, this is not always the case. Some flowers have nectar guides only visible in ultra-violet light. The video below shows how different flowers look to us (visible light), and simulates what the flowers look like to butterflies (red, green blue, and UV) and to bees (green, blue, UV).

What about pinks and purples?

Red-flowering currant (Ribes sanguineum)

It’s not uncommon to see bees visiting flowers that are colors outside of their typical pollinator syndromes. In the spring in Oregon, we see bees visiting red-flowering currants, many pink and magenta rhododendrons, plum blossoms, and cherry blossoms. Lavender, catnip, and other mint-family plants too are common on pollinator planting lists, but tend to have purple flowers.

Pollinator syndromes can help us understand these anomalies. These flowers may appear differently in ultraviolet light or may have strong nectar guides that encourage bees to visit them, despite how they look to us. Alternatively, these flowers might have rich reserves of pollen and nectar that draw bee visits.

How else do we know if a flower is a good choice for bees?

Many people have developed plant lists based on personal observations, so there are many pollinator plant lists available to choose plants from. Many nurseries include pollinator attraction information with their planting guidelines too. While these are often based on anecdotal evidence, many researchers (including Aaron and I) are working to provide empirical evidence for plant selections.

To find native plants to attract bees and other pollinators, I recommend starting your plant selections by checking out your local NRCS Plant Materials program.

Many extension programs may also have regionally-appropriate plant selections! Here is the link to Oregon State’s list of native pollinator plants for home gardens in Western Oregon.

When you’re ready to buy some plants, make sure to check out this blogpost by Aaron.

Initial survey

Determining which of these flowers are most attractive to insects is only half of the equation — I also want flowers that are attractive to gardeners. To investigate this I developed two surveys — thanks to anyone reading who took them! The first simply asked gardeners to rank the aesthetic appeal of my study plants, as well as how likely they would be to utilize them in their home gardens. This allowed me to get a baseline understanding of how appealing these flowers are for use in home gardens and landscaping.

As you can see in the figure below, many of the plants most visited by bees (highlighted in orange) were the least attractive to gardeners (Fig. 1), while plants gardeners liked the most (e.g. Iris, Columbine) were hardly visited by bees. However, its notable that many of these native wildflowers ranked around a four on a 1-5 scale, showing that these flowers do have a high potential appeal for use in landscaping!

Figure 1: Gardener ranked aesthetic appeal of study flowers on a scale of 1-5. Orange bars note plants that were consistently highly visited pollinator plants. N=587

Follow-up survey

The follow-up survey consisted of a subset of ten flowers most visited by bees, and again asked respondents to rank the aesthetic appeal and likelihood of planting for each of these flower species. Then, they were shown facts about and images of bees that visit each flower species, and asked whether they viewed each plant species more favorably, less favorably, or the same. Finally, they were asked to re-rank how attractive they found the flower species and how likely they would be to use the species in their garden, both on a scale of 1-5.

Gardener acceptance

This second survey showed a remarkable increase in gardener acceptance of pollinator friendly native plants after being educated on plant-pollinator associations. Over 80% of respondents stated that they viewed Clarkia amoena as more attractive after gain, and over 60% of respondents viewed Phacelia heterophylla, Madia elegans, and Gilia capitata as more attractive (Fig. 2).

Figure 2: Percent of respondents viewing flower species as more attractive after learning about pollinator associations. N=184.

Likelihood of planting

After learning about the benefits these flowers provide to pollinators, gardeners were also more likely to plant all ten flower species (Fig. 3). Notably, they were 40% more likely to plant Phacelia heterophylla, (a species that ranked as the least aesthetically appealing overall in the first survey). As a whole, they were also over 20% more likely to plant Solidago canadensis, Clarkia amoena. Similar increases were also observed in likelihood of planting Oreganum vulgare and Nepeta cataria. Many of the plants that showed a smaller percent change are species that started out with a higher aesthetic appeal (e.g. Gillia capitata, Lavendula intermedia, Aster subspicatus), meaning gardeners were already very likely to include these plants in their home garden before learning about the ecological benefits they provide.

Figure 3: Percent change in respondent’s likelihood of planting each top pollinator flower after learning about the pollinators associated with each. N=184

Ecological beauty

What does this all mean? This suggests that although native plants are frequently denounced as being less attractive than showy garden species, many home gardeners are still willing to use native flowers in their landscaping. Additionally, this lends credence to the concept of “ecological beauty” – that many gardeners are willing to utilize plants that will increase the habitat value and wildlife diversity in their yards.

Garden Ecology Lab

Socio-ecological research in urban and suburban garden systems

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How do we know what flowers bees like?