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Native plants are a feast for the eyes and a feast for our native bees and butterflies which need them for food and shelter.
The growing popularity of butterfly gardening has spurred sales of native plants at the garden center, and inspired gardeners across the country to add attractive native plants to support insects in our landscapes.
Research into different characteristics of native plants and their links to biodiversity is catching up to the popularity of native plant gardening.
But Mt. Cuba Center researchers can tell you one thing for sure: Changing a plant’s leaf colors to darker red or purple will stop insects from eating them.
Over three years, Mt. Cuba worked with professor Doug Tallamy, Ph.D., of the University of Delaware, to see if different kinds of cultivars affect what leaf-eating insects, like caterpillars, can eat.
What researchers found is that, with few exceptions, the ways plant breeders alter a plant’s foliage and growth habit does not appear to have an impact on a plant’s ability to feed leaf-munching insect species.
“What we did in our study was pick six traits which pretty much run the gamut of the types of cultivar traits that are selected for with regard to leaf or growth habit,” Tallamy said.
“Most cultivars are probably not discouraging insect use of the leaves. A lot of cultivars just change the habit — you take a tall, leggy plant and make it shorter — and that doesn’t seem to have any effect at all.”
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5 of 5A Web of Interconnectedness
For chewing insects, the foliage of native plants is just as important as the flowers’ nectar and pollen to a pollinator.
Newly hatched caterpillars are, as the children’s book goes, very hungry, and consume the leaves of their host plants to gain enough energy to morph into their winged adult forms.
But not just any plant will do — some insects specialize in consuming certain plants, like monarchs and milkweeds.
While milkweeds are poisonous to most insects, monarch caterpillars know how to deactivate the plant’s toxic defenses, taking advantage of a food source that other competitive species cannot consume.
While the caterpillars are munching and gathering energy for metamorphosis, birds pick off the caterpillars to feed their young. The soft, nutrient-dense flesh of these caterpillars make perfect baby food, and these young birds require a lot of food.
A single breeding pair of chickadees need to find 6,000 to 9,000 caterpillars to raise just one clutch of baby birds.
That’s a food web.
Our Yards are Habitats
The suburban yard is an important wildlife sanctuary. These wildlife interactions can only occur where there are enough native plants to sustain a food web, and our urbanization has consumed wild areas, making the residential yard the most prevalent landscape in the eastern United States.
Plant species from far-off lands dominate these cultivated landscapes and are mostly inedible to our native insects.
“Our yards need to support viable food webs,” Tallamy said. “They have to be able to pass on some of the energy they fix from the sun up the food web.”
Because most non-native plants are inedible for our native insects, they cannot pass this energy through the food web. The best way to support a food web is to plant native plants, like the keystone species that support hundreds of kinds of insects, such as oaks, native blueberry bushes and native pine trees.
Desirable Traits
Plants at the garden center are often cultivars — plants that have been specifically bred or selected for a trait that people find aesthetically pleasing in a garden setting, like plants with more flowers than the wild type, or to resist a certain disease.
Mt. Cuba Center wanted to know if any changes to the plant made them less hospitable to grazing insect life.
For this research, Tallamy compared 10 common species of native trees and shrubs and their cultivars that were bred for six popular traits:
• Red or purple leaf color
• Variegated leaf color
• Growth habit
• Disease resistance
• Fruit size and yield
• Fall color.
Volunteers planted these species in a grove at Mt. Cuba Center.
“All the plants we were studying are in the same ecological place, and they’re all growing in the same conditions,” Tallamy said. “Any insects coming in choose between a cultivar or a straight species — you’re not dealing with different insect populations, or different plant treatments.”
After letting the plants grow and establish themselves for one year, three research methods were performed. Three times each summer, researchers vacuumed insects off the plants to count the numbers and species of insects present.
Next, they took samples of each plant’s leaves into a laboratory to observe how much of each leaf insects — in this case, newly hatched bagworms — ate, and which plants they preferred.
Finally, they measured a plant’s overall appeal by collecting 20 leaves from each plant at the end of the season and then scanning them into a computer program to use precise tracing and measuring tools to estimate how much of the leaves had been consumed during the season.
Red means stop
After analyzing the data, the only trait that consistently deterred insects from feeding on it was turning foliage darker red or purple.
“Changing the leaf color changes the leaf chemistry,” Tallamy said. “Leaf chemistry is how insects find the plant, and how they relate to it. They are physiologically tuned-in for the chemistry of their host plant.”
So changing the chemistry may make the plant unrecognizable to the insects that depend on it.
Further study
The research study focused on the foliage, habit and disease resistance of cultivars of native plants, and did not investigate the effects from changed flower size, color and shape that many cultivars bring to the landscape.
“It becomes much more of an ‘it depends’ situation,” Tallamy said. However, when shopping for foliage value, concerned gardeners can rest assured that many popular changes to a plant have little impact on its ability to support our insect neighbors.
If you go
WHAT: Mt. Cuba Center’s annual Wildflower Celebration, including native plants, live music, arts and crafts
WHERE: Mt. Cuba Center, with parking available at 1003 Old Wilmington Road, Hockessin
WHEN: 10 a.m.-4 p.m. Sunday April 28
ADMISSION: Free
FOR MORE INFO: Go to mtcubacenter.org
Nature’s Landscapes is an occasional column by Mt Cuba Center, a botanical garden located in Hockessin, Delaware. This column was written by Katie Bohri, the communications manager. The center opens for general admission on April 3 and offers classes year-round. For more information, go to mtcubacenter.org.
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