hawkmoth – My Chicago Botanic Garden

Evening Primroses, Pumps, and Pollinators

Rick Overson is fascinated with insects—especially the kinds that love desert climates like in Arizona, where he grew up and earned his Ph.D. in biology. After completing a postdoctoral assignment in northern California, he decided it was time to get to know the little buggers even better, so Dr. Overson hopped on a plane for Chicago and stepped out into the subzero temperatures of the polar vortex to do just that.

PHOTO: Dr. Rick Overson with hawkmoth specimens. — Dr. Rick Overson with hawkmoth specimens

The devoted entomologist didn’t expect to see the insects in Chicago, but he was eager to join research at the Chicago Botanic Garden. A multidisciplinary team was assembling there to look for scent variations within Onagraceae, the evening primrose family, and connections from floral scent to insect pollinators and predators. The findings could answer questions about the ecology and evolution of all insects and plants involved. Overson is a postdoctoral researcher for the initiative, along with Tania Jogesh, Ph.D.

“Landscapes of Linalool: Scent-Mediated Diversification of Flowers and Moths across Western North America” is funded by a $1.54 million Dimensions in Biodiversity grant from the National Science Foundation. The project is headed by Garden scientists Krissa Skogen, Ph.D., Norman Wickett, Ph.D., and Jeremie Fant, Ph.D. It was developed from prior research conducted by Dr. Skogen on scent variation among Oenothera harringtonii plants in southern Colorado.

“For me, the most important thing coming out of this project is documenting and showing this incredible diversity that happens inside a species,” said Overson. “It’s vitally important for me to break down this idea of a species as a discrete unit. It’s a dynamic thing that is different in one place than another. That factors into conservation and our understanding of evolution.” In this case, he and his colleagues theorize that the evolution of the insect pollinators and predators is connected to the evolution of the scent of the plants.

The first two years of field work brought Overson back to his desert home. He traveled across Arizona, Utah, and nearby states with a group of about five scientists during summer months when the flowers were blooming. The team visited several populations each of 16 species of flower for a total of 60 locations. Overson and the team identified and documented the insects visiting the plants and compiled scent chemistry from the flowers. Their tool kit included a pump to pull the scent from a flower onto tiny polymer beads that held the scent inside of a vial. From there, they extracted the scent chemicals at the end of the research day or night. “It’s definitely the case that this pattern of scent variation inside a species is very common in this group,” he said of the team’s preliminary findings.

PHOTO: Hawkmoth on evening primrose. — A beneficial pollinator, the hawkmoth, visits an evening primrose (*Oenothera harringtonii*).

In the field they also took video recordings of pollinator behavior to see who visited which flowers and when. The pollinators, including hawkmoths and bees, follow scents to find various rewards such as pollen or nectar. The insects are selective, and make unique choices on which plants to visit.

Why do specific pollinators visit specific plants? In this case, the Skogen Lab is finding that it is in response to the scent, or chemical communication, each flower releases. “In the natural world those [scents] are signals, they are messages. Those different compounds that flowers are producing, a lot of them are cocktails of different types of chemicals. They could be saying very different things.”

PHOTO: Closeup of a wasp on a closed evening primrose bloom. — Nature is complicated. Here, a wasp lays eggs through a flower bud into a hidden Mompha moth inside. Its larvae will eventually destroy both the moth and the flower. Photo by Dr. Rick Overson

A destructive micromoth called a microlepidopteran (classified in the genus Mompha), has also likely learned how to read the scent messages of its hosts. The specialist herbivore lays eggs on plants leading to detrimental effects for seed production. The team’s field work has shown that Mompha moths only infect some populations of flowers. When and why did the flowers evolve to deter or attract all of these different pollinators? Or was it the pollinators who drove change?

At the Garden, Overson is currently focused on exploring the genomes, or DNA set, of these plants to create a phylogeny, which looks like a flow chart and reads like a story of evolution. “Right now we don’t know how all of these species are interrelated,” he explained. When the phylogeny is complete, they will have a more comprehensive outline of key relationships and timing than ever before. That information will allow scientists to determine where specific scents and other traits originated and spread. He will explore the evolution of important plant traits using the phylogeny including the color of the flowers and their pollinators, to answer as many questions as possible about relationships and linked evolutionary events.

In addition, the team is looking at population genetics so they can determine the amount of breeding occurring between plant locations by either seed movement or by pollinators. They will also look for obstacles to breeding, such as interference by mountain ranges or cities.

“Relationships among flowering plants and insects represent one of the great engines of terrestrial diversity,” wrote principal investigator Krissa Skogen, PhD, in a blog post announcing the grant.

The way that genes have flowed through different populations, or have been blocked from doing so over time, can also lead to changes in a species that are significant enough to drive speciation, or the development of new species, said Overson. “The big idea is that maybe these patterns that are driving diversity within these flowers could ultimately be leading to speciation.”

By understanding these differences and patterns, the scientists may influence conservation decisions, such as what locations are most in need of protection, and what corridors of gene flow are most important to safeguard.

PHOTO: Dr. Rick Overson in the field. — Dr. Rick Overson in the field

“We absolutely can’t live without plants or insects, it’s impossible,” remarked Overson. “Plants and insects are dominant forces in our terrestrial existence. Very few people would argue that we haven’t heavily modified the landscape where these plants and insects live. I think it is crucially important to understand these interactions for the sake of the natural world, agriculture and beyond.”

When Dr. Overson is taking a break from the laboratory, he visits the Desert Greenhouse in the Regenstein Center, which feels like home to him.

Filming “Plants Are Cool, Too!”

This past spring I was asked by a friend and colleague, Chris Martine, to be featured in an upcoming episode of Plants Are Cool, Too!

A few months later, in August, we taped episode 4, focusing on my work with plants and pollinators, and episode 5, which will feature the work of Mike Moore of Oberlin College on gypsum-endemic plants (to be released later this year).

PHOTO: Chris Martine and cameramen filming against New Mexico scenery. — Chris Martine shoots the intro to *Plants Are Cool, Too!,* episode 4. (Photo: Krissa Skogen)

So what exactly is Plants Are Cool, Too!?

Chris Martine created the web-based series Plants Are Cool, Too! to address a gap in the nature show genre: there are no shows focused explicitly on plants that might engage people, from elementary school kids on up. He set out to create a series focusing on some of the coolest plants, their stories, and the scientists who study them. As of today, four episodes have been released:

Episode 1 — The Pale Pitcher Plant
Episode 2 — Fossilized Forests
Episode 3 — Undead Zombie Flowers of Skunk Cabbage
Episode 4 — Desert Plants and Marathon Moths (my show—see it at the end of this post!)

Adventures with botanists and filmmakers

So what does it take to create an episode? And how about two episodes at once, in just three days? Certainly, lots of planning, people who know the lay of the land, and a fantastic film crew. Thankfully, Chris is really good at what he does—the team of people he pulled together couldn’t have been better.

PHOTO: Hartweg's sundrops blooming at dusk. — The star of the show: Hartweg’s sundrops (*Oenothera hartwegii* spp. *filifolia*), a night-blooming member of the evening primrose family. (Photo: Krissa Skogen)

Our first site for filming was Yeso Hills, just southwest of Carlsbad, New Mexico. We arrived at the golden hour, when the sun is near the horizon and casts a golden light on everything. As we turned off the highway onto a gravel road, we encountered a sea of sundrops (Oenothera hartwegii and O. gayleana). I had a hard time containing my excitement. I’ve seen photos of populations like this, but nothing like it in person. There were plants everywhere, hundreds of them, their yellow flowers on full display, glowing magnificently in the setting sun. I suspected it would be a fantastic night for hawkmoths—how could they not be drawn to this fantastic population? So many plants, so much nectar! It was going to be awesome.

PHOTO: Setting up cameras on the dunes as the sun sets. — Here, we are setting up the site that will be filmed. (Photo: Patrick Alexander)

Until it wasn’t.

The sun set and we taped a handful of things: setting up the “moth sheet,” collecting floral scent, nectar, size measurements. And we waited and waited for the hawkmoths to show up; after about two and a half hours, we headed toward Carlsbad for the night. While I couldn’t imagine a better place for a hawkmoth to be, they clearly could.

PHOTO: Setting up a moth-catching framework at dusk. — Setting up the “moth trap”–a PVC frame with a bedsheet stretched over it. At night, a blacklight is turned on to attract night-flying insects (incuding hawkmoths) to the sheet. (Photo: Tim Kramer)

PHOTO: Cameraman filming the moth trap setup as the sun sets on the dunes. — In the dusky light we filmed the setup of our moth trap. (Photo: Tim Kramer)

PHOTO: Visitor Center entry to White Sands National Monument — White Sands National Monument (Photo: Krissa Skogen)

The following morning, we headed for White Sands National Monument, home of the world’s largest deposit of gypsum sand dune field, just west of Alamogordo, New Mexico. August 21 was a special night at White Sands—Full Moon Night. The park stays open until 11 p.m., and visitors come from near and far to experience the magic of the white sands by moonlight—which was one of the main reasons we were there. The flowers of the Hartweg’s sundrops glow in the moonlight and are very easy to see when the moon is full, by us as well as their hawkmoth pollinators.

After checking in with the National Park Service office, we set out to find Hartweg’s sundrops. The dunes provided the perfect white backdrop to capture hawkmoths visiting the flowers. Usually it’s hard to follow an individual moth at dusk; they become lost in the vegetation unless they’re quite close to you. At White Sands, you could follow an individual hawkmoth easily, from flower to flower, plant to plant—that is, if they showed up.

PHOTO: Sunset at White Sands National Monument. — The sun sets at White Sands National Monument–we eagerly anticipate the arrival of the moths and the full moon. (Photo: Krissa Skogen)

For a second night, we were out at the golden hour. Everything was beautiful, bathed in the light of the setting sun. We were feeling optimistic. Considering that this was our last chance to capture moths on film, we were prepared to stay as late as necessary. Looking around at everyone, I realized just how lucky I was, how lucky we all were to be there, together, at this incredible place, on what was sure to be an incredible night. Could we also be so lucky as to be graced by the presence of hawkmoths? We had come so far to capture this moment, and I have experienced many nights when conditions seemed ideal for hawkmoths to show up, only to be stood up instead—like the night before, at Yeso Hills.

PHOTO: Filming the episode in the dark. The moth trap provides a backlight for the "cast." — Krissa and Chris catch hawkmoths and discuss their role in pollination of Hartweg’s sundrops and other night-flowering plants. (Photo: Tim Kramer)

Before long, the sun had dropped over the horizon and the timing seemed right. I mentioned to Chris that I wouldn’t be surprised if we started to see some hawkmoths. As if on cue, a moth flew right by Chris’s head, close enough for him to hear its papery wings fluttering about—all as the camera was rolling! To say I was excited is an understatement. One moth turned into two…three…six…ten—visiting flowers, drinking nectar, and picking up pollen on their tongues, faces, and bodies, moving it from flower to flower—doing the ever-so-important job of pollination. You see, these plants will not produce fruits or seeds on their own—they require pollen from a different plant to do so, and that pollen has to be transported by a pollinator.

So after much nervous anticipation, the hawkmoths had arrived. And now you can see the full episode and how our adventures fit together into a nice story about desert plants that flower at night and their hawkmoth pollinators!

PHOTO: Pinned specimen of Hyles lineata. — White-lined sphinx moth (*Hyles lineata).* Just after sunset, a number of moths started to visit flowers, as if on cue! (Photo: Krissa Skogen)

Many thanks to Chris, Tim, and Paul, for being so incredibly fantastic to work with, and Mike, Norm, Hilda, Helga and Patrick, from whom I learned a great deal about the New Mexico flora and gypsum endemism. Thank you to Sophia Siskel and the Chicago Botanic Garden for providing financial and institutional support. This trip was truly the experience of a lifetime.

Science Scents

Summer romance is in the air on the shortgrass prairie of southeastern Colorado. Quite literally, the alluring fragrance of Harrington’s evening primrose (Oenothera harringtonii) wafts in the breeze when the plant blooms each evening. Insects from bees to moths follow the scent to the flower of their dreams.

Dr. Skogen sets up floral-scent collection equipment for a previous experiment at the Garden.

The insect’s choice of flower is significant to the future of the plant species, according to Krissa Skogen, Ph.D., Chicago Botanic Garden conservation scientist. After a pollinator lands on a plant and sips its nectar, it may carry a copy of a plant’s genes, in the form of pollen, to the next plant it visits. That next plant may then take those genes to combine with its own to form a seed—creating the next generation of Harrington’s evening primroses.

How do pollinators select a flower? According to Dr. Skogen, floral scent heavily influences their choices in addition to floral color and size. “Floral scent is this fascinating black box of data that a lot of reproductive biologists haven’t yet collected,” she said.

Mothmatics
After studying the many pollinators of the evening primrose, from bees to moths, she found that two species of moths called hawkmoths—or more specifically, the white-lined sphinx moth (Hyles lineata) and the five-spotted hawkmoth (Manduca quinquemaculata)—are most effective. She told me that 30 percent more seeds are produced when a hawkmoth pollinates a plant rather than a bee.

Dr. Skogen and her team start their evening pollinator observations at dusk in Comanche National Grasslands.

“What’s really awesome about this system is that these hawkmoths can fly up to 20 miles in a night, while bees typically forage within one to five miles,” she added.

An insect so large it is often confused for a hummingbird, the brown-and-white hawk moths can carry genes between the widely spaced evening primrose populations.

A five-spotted hawkmoth visits Harrington’s evening primrose near Pueblo, Colorado.

In fact, Skogen has genetic data that support this idea—the roughly 25 populations she and her colleagues have studied throughout southeastern Colorado really act as two to three genetically, because the hawkmoths do such a great job moving pollen over long distances.

Making Sense of Scent
How do the hawkmoths use floral scent to decide which flower to visit? According to Skogen, they detect scent at a distance in the air with their antennae as they fly. (Once they get closer, flower color and size become more important in locating individual flowers.)

Skogen and her colleagues have determined that flowers in some populations smell very different from each other, and these differences in fragrance can be detected by humans. Fragrance combinations include green apple, coconut, jasmine, and even Froot Loops™.

Skogen’s theories suggest that differences in floral scent may direct female white-lined sphinx moths to the best host plants for their eggs, attract enemies (including seed-eating moths), reflect differences in soil, or the floral fragrance of other plant species flowering nearby.

The white-lined sphinx moth drinks nectar from Harrington’s evening primrose in Colorado.

Fielding Questions
What combinations of genes create the scents that best attract the hawkmoths? What do the genetic data of existing plants tell us about the direction genes have moved in the past? Are other insects, such as herbivores and seed predators, helping to move pollen or inhibiting reproduction?

These are the questions Skogen and her research team, including the Garden’s Jeremie Fant, Ph.D., and students Wes Glisson and Matt Rhodes, will investigate further. Late this summer and in future fieldwork, they will monitor the pollinators and collect floral and plant-tissue samples.

Back in the Harris Family Foundation Plant Genetics Laboratory and the Reproductive Biology Laboratory at the Garden, they will compare the genetic data of these plants with the observed patterns of the pollinators, and other floral data.

Each trip is another step closer to having a positive impact on the future of the state-imperiled evening primrose and its choice pollinators. This species is endemic, growing only in southeastern Colorado and northern New Mexico where the unique soils best suit its needs.

Learn more about Dr. Skogen’s work and watch a video.

Because the species grows in limited locations and is easily thwarted by the impacts of development, climate change, invasive weed species, and other intensifying threats, it’s especially important that its future generations are strong.

Skogen’s love for nature has been lifelong. As a child in Fargo, North Dakota, she enjoyed playing in unplowed prairies. Now, at the Garden, she visits Dixon Prairie as often as she can. “There is beauty in the natural distribution of species,” she said. “The prairie habitat is imprinted on me from those childhood experiences. It feels like home.”

Coloring Between the Lines

As dusk fell over Illinois State Beach Park, Jeremie Fant, Ph.D., perched silently beside the rare downy Indian paintbrush. He watched as the white-blooming Castilleja plant opened its tubular flower and emitted a sweet scent. The clock ticked past 6 p.m. Cautiously, a moth appeared out of the night sky, and fluttered over to sip the plant’s nectar. Bingo.

That moment, and subsequent research in Illinois and Colorado, led Dr. Fant, a molecular ecologist with the Chicago Botanic Garden, to become the first to document the moth as a pollinator of Castilleja with Krissa Skogen, Ph.D., his research partner and a conservation scientist at the Garden.

Dr. Fant in the field — Dr. Fant conducts fieldwork in the Comanche National Grasslands in Colorado.

Fant studies the importance of how flowers are designed to attract specific pollinators, and what a plant’s pollinator means for its survival as a species. “I am fascinated by the way these events can lead to permanent impacts on a plant population,” he said.

He recently explained the intricacies of the process to me, and why the palette of colors we see in the Garden and elsewhere is not only beautiful, but also functional.

The Palette of Pollinators
Pollinators—such as bees, birds, flies, and moths—offer specific benefits to plants, according to Fant. Birds travel expansive geographic areas, and can spread the pollen of a single plant over a large area. Bees, on the other hand, are more localized in their foraging, covering more plants in a condensed area. Where moths fall in this spectrum is not known: they may diversify the genes in a plant population by carrying pollen further than bees, but they may not travel as far as birds.

“The imprint left behind from genealogy is stamped on the landscape, and it’s my job to figure out how that pattern got there,” said Dr. Fant.

Plants Spin the Color Wheel
A flowering plant puts a lot of energy into producing a flower. Why? The purpose of flowers is to attract pollinators who will spread the plant’s genes— promoting the continuation of the species, said Fant. When a plant is red, it attracts birds as pollinators, but if it is yellow, it attracts bees. White flowers are particularly appealing to moths—especially those that bloom after sunset when moths are out and about. The color, combined with the scent, allows a plant to lure in a specific pollinator.

Connecting the Dots
This information led to a hunch when Fant considered the white flowers on the downy Indian paintbrush in Colorado and at Illinois State Beach Park, where he conducts much of his fieldwork. Most species of Castilleja plants produce red flowers and are known to be pollinated by birds. But here in Illinois, in the furthest east population of such plants, they chose a different color, and as he confirmed, a different pollinator. It is the question of why, and what that choice means for the plant, that Fant is now preparing to study when he returns to his field research this spring.

prairie aug-2574 — Charismatic red flowers bloom on the gravel hill in the Dixon Prairie, Fant’s favorite area at the Garden.

Ultimately, Fant tracks how genes move within plant populations, which largely hinges on how they are carried by pollinators. He examines plant DNA to determine if they share one or more genes, and are therefore related. Then, he maps the location of related plants, tracking the movement of specific genes and inferring how and why they got there. “There’s always some reason for the movement,” he said.

This spring and summer, look for red flowers on the gravel hill in the Dixon Prairie, where Dr. Fant is growing unique bird-pollinated plants such as the royal catchfly, with the goal of increasing the plants’ genetic diversity.

Fant noted that moths are often overlooked as pollinators, and along with Dr. Skogen he is especially interested in studying their relationship with many kinds of plants. In addition to the Castilleja, he also studies rare species of the gravel hill in the Garden’s Dixon Prairie.

At the end of our conversation, Fant, dressed in a bright-yellow sweater, jumped up from his desk and headed toward his lab in the Daniel F. and Ada L. Rice Plant Conservation Science Center, where he is always moving forward to catch up with the past.