By Ronica Stromberg, National Research Traineeship Program Coordinator
Miyauna Incarnato, doctoral researcher at the University of Nebraska-Lincoln, has discovered that studying monarch butterflies is not for the faint of heart.
For one thing, eastern monarch butterflies are hard to track. The orange-and-black beauties breed four to five generations in a year, with successive generations migrating from Mexico to Canada and back again. Depending on where and when they are born, the butterflies live for different lengths of time. Only adults live in Mexico, where they are thought to live eight to nine months, mostly in diapause. Butterflies hatched from eggs laid along the migration route may live only a few weeks. How does a two-legged scientist in Nebraska track all of that?
Complicating matters further, monarch populations have rapidly declined since the mid-1990s, with a recent count in Mexico estimating decline at 85 percent. Monarchs are now on the waiting list to be considered for Endangered Species Act protection.
In August 2021, Incarnato came to UN-L from Ohio to study butterflies. Seeing both the peril that monarchs face in the wild and the need to understand them better, Incarnato decided to take monarch caterpillars bred in the lab of her home department, the School of Biological Sciences, and experiment with them outdoors.
“Rearing monarchs outside is difficult, but I didn’t want to jeopardize wild populations by removing valuable monarchs from them,” she said.
With the help of her university advisors, Kristi Montooth and Ana Maria Vélezand, and Sandy Montooth, a quilter in Lincoln, Incarnato built cages to house the lab caterpillars outdoors — something she had not heard of being done before.
In a trial run in spring 2022, Incarnato placed 15 caterpillars out on milkweed, the only plant they eat, under cages on a prairie outside Lincoln. All 15 survived to adulthood.
In the summer and fall, she placed 150 caterpillars at six sites, with each site having five cages with five caterpillars in each. Three of the sites were within Lincoln, including an East Campus site, and three were in prairies outside Lincoln.
“What we actually saw, some of my more preliminary results, is survival was significantly higher at prairie environments,” Incarnato said.
The prairie monarchs also grew larger and had more eggs in their ovaries than the urban monarchs.
However, the overall survival rates to adulthood for the caged monarchs were much lower than in the lab, where it averaged 60 percent. The prairies sites averaged about 38 percent survival, and urban sites averaged about 13 percent.
Urban sites may have been watered, but prairie sites were not. When drought struck, the milkweed on some prairie sites died. Without healthy milkweed leaves to eat, the prairie caterpillars at those sites died.
“This isn’t like a cut-and-dried which one is better,” Incarnato said of the prairie and urban sites. “It’s examining what are the consequences we’re going to have to deal with in the different environments.”
Past studies have suggested monarchs are chiefly affected by temperatures and seasonal changes in the length of the day, Incarnato said. She plans to continue looking at these factors when she runs field and lab experiments over the next two years. Incarnato also collected all the dead caterpillars, hatched butterflies and milkweed leaves to look at other factors like exposure to pesticides, fungicides, herbicides or bacterial disease.
Factors she cannot examine in her experiments include highway deaths and parasitoid wasps. Incarnato said past studies have suggested many monarchs died trying to migrate across large highways in Texas and Oklahoma.
Parasitoid wasps kill monarchs by laying eggs in them, causing them to “explode” when the eggs hatch, Incarnato said. Her cages kept parasitoid wasps out.
Squirrels were another matter. She discovered three cages knocked over and a hole chewed into one of them. Not to falsely accuse squirrels, but she did find a squirrel sitting atop one of her cages when she checked on it.
Then Nine-Mile Prairie caught on fire, and the fire ended about 5 feet from her cages.
None of these obstacles deterred Incarnato. She sees the eastern monarch population as one the world can’t afford to lose, with the butterflies making up about 99 percent of all North American monarchs.
“If this species’ population continues to decline and is eventually lost, we really may be actually losing an entire genetic component important to their migration, and this is also the largest population that feeds into the populations across the world,” she said. “So, for the resilience of the monarch species, it’s very important to both understand and make sure this larger migrating population isn’t compromised.”
A smaller population of western monarchs migrates between the states of Washington and California, and eastern monarchs feed into that population, Incarnato said. Nonmigratory monarchs can be found around the world, in places like Columbia, Cuba, Puerto Rico, Australia and parts of Europe, and they are not necessarily in danger.
For the imperiled eastern monarch, though, Nebraska is, as Nebraskans like to say, “in the middle of everywhere.”
“Nebraska is really midway,” Incarnato said. “So, we see a lot of a lot of monarchs throughout the entire season, versus way north they don’t see them until later in the summer in a much shorter period, which is why Nebraska is a really cool place to study monarchs. Right in the middle.”
Nebraska also is known for quick weather changes, which Incarnato said may help her better understand how temperature variance stresses monarchs.
“If it’s too hot, and a monarch is like, ‘Whoa, it feels like June,’ but it’s actually October, I’m concerned that maybe they won’t get the environmental triggers to migrate back down to Mexico,” she said. “They will sit here, and then all of a sudden, it’s freezing rain outside. They didn’t realize they had to go back.”
Other scientists have questioned how she will be able to draw conclusions about wild monarchs from lab monarchs. She has responded by adding another part to her experiments by breeding wild monarchs with the lab ones.
“You can’t say they are 100 percent the same, so I try to mitigate that by rearing them outside, but I’m also going to try to mitigate that even more by introducing wild monarchs into the lab population to introduce new genes into our lab population and do the experiment again with those,” she said.
The captured monarchs and their offspring will become lab monarchs, unsafe to return to the wild.
Looking toward her own future after she graduates, Incarnato said she would like to work at a place where she can do research and engage with the public. She said she is more interested in conservation and its management than studying a particular species, though she has found studying monarchs in Nebraska interesting.
“They’re very charismatic, they’re widespread and they’re very noticeable. People recognize them,” she said. “So, they are a great tool for helping convey conservation decisions, management decisions and the importance of conservation as a whole.”