A Bee’s Eye View: UV photography and bee vision

Flowers and bees have one of the most well-known symbiotic relationships ever formed. Flowers rely on bees for pollination, and bees rely on flowers for nectar and pollen. It is generally understood that flowers act as advertisements to attract bees. However, less is known about what exactly bees are seeing and how that can change once humans get involved. This project is focused on the changes that can arise after a plant is cultivated, and how these changes can affect pollinator preference of a flower.

While changes made by breeders might not seem all that drastic to our eyes, we have little idea if that is the case for bees. Often breeders will change flowers for aesthetic purposes. This can have unknown consequences. These changes might not seem like such a big issue since the flowers are still colorful. However, bee vision is very different from humans, with bees having the ability to see into the UV spectrum. This means that while we might think we are only changing the bloom size or the color, we could also be unintentionally changing UV messaging visible only to the bees.

The purpose of this study is to use UV photography to explore these invisible differences between the native and cultivar. We also want to determine if the differences have a tangible impact on pollinator preference. This study is ongoing, but the images so far have shown a few native/cultivar sets that have a marked difference in UV markers between native and cultivars. While the study has only just started, our excitement and curiosity have not abated. This is an entirely new foray into pollinator relationships and mechanisms and could open up the world of bees and flowers in a brand new way.

An example of a UV photo of a nemophila flower, with a UV marking in the center, highlighted in blue

How do we know what flowers bees like?

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.

Blue Flax (Linum lewissii)
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

TraitBeesButterflies
ColorWhite, yellow, blue, UVRed, purple
Nectar GuidesPresentPresent
OdorFresh, mild, pleasantFaint but fresh
NectarUsually presentAmple, deeply hidden
PollenLimited; often sticky or scentedLimited
Flower ShapeShallow; with landing platform, tubularNarrow 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.

2019 Native Plant Field Season Update

I’m thrilled to announce that this summer I completed the third field season of my study. This is slightly bittersweet – while I’m excited that we are done with hot fieldwork, I will miss chasing bees around the farm and the view of Mt. Hood. I’m incredibly thankful for this third season of data, as it will help account for some of the temporal variation inherent in ecological studies. In fact, pollinator communities in particular tend to be highly variable both within and across field seasons. Having three seasons of data will hopefully allow us to identify more reliable patterns of pollinator visitation between my study plants.

Lots of lab work remains, as I’m tackling the insect samples that we collected with the bee vacuum. With the help of a dissecting scope, I’m attempting to identify the each specimen to at least the taxonomic level of family to get a sense of the broader insect communities associated with each flower species in my study. It will be several months before I can share this species-richness data, but in the meantime I have bee abundance data to share with you!

Aaron and Lucas in the native plant study site, in 2017. You can see the 1m by 1 m plot in the foreground by Aaron, a second one near Lucas, and a few more in the distance.

As a refresher, we performed timed pollinator observations at each plot. This consisted of observing each blooming plot for five minutes and counting all the insects that landed on open flowers. Bees were sorted to “morpho-type” (honey bee, bumblebee, green bee, and other native bee). Though this doesn’t give us species-level information on the floral visitors, it allows us to understand which plants attracted the most pollinators overall, and allows us to detect any patterns of visitation between honey bees, bumblebees, and solitary native bees. Below is a summary of some of the highlights.

2019 overall bee abundance by plant species:

  • Origanum vulgare, Lavendula intermedia, and Eschscolzia californica were top five bee plants in 2019, just as they were in 2018.
  • In 2019, Phacelia heterophylla and Solidago canadensis jump into the top five, while Nepeta cataria and Gilia capitata fall out of the top five. It should be noted that Nepeta was the sixth most attractive plant, with about the same visitation level as Solidago.
  • Again, similar to 2018, it appears that honey bee visitation was driving the high visitation rates of the popular exotic garden species (marked with a red asterisk), while native wildflowers were being visited more frequently by native bees.
  • I’ve included the 2017 and 2018 overall abundance graphs as well, for comparison. You can see that the overall abundance was higher in 2019 for the two most popular plants, at about ~25 bees per observation period!

2017 overall bee abundance by plant species:

2018 overall bee abundance by plant species:

Since honey bee visitation drove the high abundance of many of the top pollinator plants, I took honey bee visits out of the data set and made a new graph, to compare which plants were most attractive to native bees.

2019 native bee abundance by plant species:

As you can see above, honey bees are excluded from the analysis, the top five most popular plant species completely reshuffles.

I’ve included that 2017 and 2018 native bee abundance data below for comparison.

2017 native bee abundance by plant species:

2018 native bee abundance by plant species:

Please stay tuned for more updates on the bee species richness we collected in 2019, as well as data on the other insects (pests and natural enemies) that we collected!

Isabella Featured on Pollination Podcast

Isabella Messer has been a member of the Garden Ecology Lab for more than two years, where she primarily assists with the garden pollinators study, but will is also developing her own research project. Her independent research project will look at bee visitation to some of the plants we are studying in controlled research trials, when these same plants are in a mixed garden setting. Controlled research trials are important, because they let us document the attractiveness of plants to bees, in a setting where study plants are not competing with other plants for pollinators. Controlled research trials are also valuable, because they let  researchers have better control over environmental conditions, such as irrigation. Isabella is going to see whether and how bee visits on plants in a garden context is different than what Aaron is documenting in his controlled research trials. This will be one of the first, if not the first time, that we will have direct and contemporaneous measures of bee visits on focal plants in each situation: in a research field, and in a garden.

In addition to her work in the lab, Isabella is also a member of the ‘Research Retinue’: a group of Oregon State University undergraduates, who review and discuss papers on the PolliNation Podcast.

In this episode, the retinue discusses two papers that look at the impact of a common herbicide (glyphosate) on bees, via indirect impacts of glyphosate on the microbiome (bacterial community) that can be found in honey bee guts.

The paper that they discuss is linked, below: