I thought I was doing the right thing. When I moved into my house 11 years ago, I found a purple barberry shrub (Berberis thunbergii) planted in the back yard by the previous owner. I thought right away, it had to go. I knew Japanese barberries, so commonly planted in landscapes, were escaping into natural woodland areas and creating dense thickets to the exclusion of native plants. These thickets have been shown to make suitable habitat for Blacklegged Ticks. I wanted no part in contributing to that situation, so I donned my work gloves and removed that prickly beast of a shrub.
In the barberry’s place, I planted a “native” purple-leaf ninebark, Physocarpus opulifolius ‘Diabolo’. It had deep burgundy foliage that made a nice replacement for the burgundy-toned barberry. And, I was selecting a Maryland native plant. I thought it was a perfect choice.
I sang praises about this ninebark for years when people asked me for native plant recommendations. It has great spring blooms, beautiful foliage color, and I never had to prune it. And native plants support native insects so I was doing a good thing to help wildlife. I was doing the right thing!
Or so I thought.
It was just this year that I learned from my colleague, native plants specialist Dr. Sara Tangren, that this particular cultivar of the native ninebark was actually detrimental to a specific native insect, the Ninebark Leaf Beetle. My heart just sunk when I heard this. I am first and foremost a plant enthusiast, but I also appreciate insects—the essential roles they play in our world as well as their often stunning beauty. And when I looked up the Ninebark Leaf Beetle, I discovered that it is indeed a beauty. And then my heart sunk even further. My purple ‘Diabolo’ ninebark, it turned out, was no good for this native beetle. The alteration in the leaf color – changing the green of the native species to the burgundy of the cultivar – makes it distasteful to the beetle.
The effects of altered leaf color on plant-feeding insects was noted in a new study published in HortTechnology magazine last month. The authors (Baisden et al.) conducted experiments on several native woody plant cultivars compared to the straight natural species. They looked at whether six altered traits in the cultivated varieties – leaf color, variegation, fall color, growth habit, disease resistance, and fruit size – had any effect on insect feeding, development, and abundance.
In all three experiments they conducted, the researchers found that the cultivars with leaves that were altered from green to red, blue, or purple deterred insect feeding. Results were not consistent for the other cultivar traits they tested.
There are a couple hypotheses as to how leaf color affects insect feeding. Most plant pigments are compounds that do not contribute to the growth of a plant. They may instead provide a defense mechanism. Anthocyanin pigments make a red coloration that may warn insects that the plant has defensive, distasteful chemicals – and they stay away.
The question of whether cultivars of native plants – nativars – have positive or negative effects on native wildlife is an active and ongoing area of research. Results in past studies have been mixed. (For more on this topic, see Mt. Cuba Center research).
I know how appealing it is to choose plants with special characteristics – the colored foliage, bigger flowers, the more compact form or general appearance that suits my personal taste. But my choices may not, in some cases, be to the taste of other things in our environment and the things that depend on them for food. It is a dilemma. I do like specific non-native plants (I’ll never give up my dahlias), but I also adore the lilting songs of chickadees in the springtime. Many birds like Carolina chickadees need caterpillars to feed their young and many caterpillars can only feed on wild, native plants. See New Smithsonian Study Links Declines in Suburban Backyard Birds to Presence of Nonnative Plants. I should note that a different study (Craves) found that native birds, including chickadees, were able to find insect food on non-native, invasive Amur honeysuckles. (Which makes the issue even more confusing, right?)
“When we try to pick out anything by itself, we find it hitched to everything else in the Universe.” – John Muir
For an ecologically minded gardener, it feels complicated to sort this all out and do the right thing. I felt disappointed that my ‘Diabolo’ ninebark was a missed opportunity to support a particular native insect, but, as Dr. Trangren explained to me, it becomes more of a problem when cultivated nativars cross-pollinate with the wild species and change the genetics of the native populations, making them less capable of supporting insects on a broader scale. For this reason, she recommends choosing cultivars that are sterile.
It was a lesson learned and one that makes me more thoughtful about my plant choices and their broader impacts.
By Christa K. Carignan, Maryland Certified Professional Horticulturist; Coordinator, University of Maryland Extension Home & Garden Information Center.
Craves, Julie A. 2017. Native birds exploit leaf-mining moth larvae using a new North American host, non-native Lonicera maackii. Écoscience, 24:3-4, 81-90.
Baisden, Emily C., Douglas W. Tallamy, Desirée L. Narango, and Eileen Boyle. 2018. Do cultivars of native plants support insect herbivores? HortTechnology 28(5) 596-606.
Narango, Desirée L., Douglas W. Tallamy, and Peter P. Marra. Desirée. 2018. Nonnative plants reduce population growth of an insectivorous bird. Proceedings of the National Academy of Sciences of the United States of America.
Learn more about native plants on the University of Maryland Extension Home & Garden Information Center website.
In the 1900s, Nikolai Vavilov studied botany and agriculture. He researched ways to make crop plants more disease resistant, drought tolerant, and higher yield. Working on behalf of the Institute of Plant Industry in Leningrad, he and his staff traipsed through villages, jungles, and savannahs around the world, collecting seeds from crops and their wild relatives. They were after the genetic diversity needed to breed new crop varieties. There was an urgency to their work; as populations of heritage varieties and wild plants cross-pollinated with modern cultivars, precious genetic diversity was lost. Their hard-won collection constituted one of the world’s first seed banks.
During World War II, Hitler’s troops laid siege to Leningrad for two and a half years. Many citizens died as the result of air raids, artillery fire, and in the second winter, as many as 100,000 people died of starvation each month. The scientists of the seed bank secreted parts of the collection away and took shifts protecting the remainder. As food became scarce, they pledged to each other never to eat the seeds in the collection. The seed collection survived, but nine of the scientists starved to death, surrounded by envelopes of beans, corn, oats, wheat, and rye.
The effort to secure the DNA of the world’s flora in seed collections continues today. Here are the world’s largest seed banks and how they continue the struggle to save the DNA needed to protect the future of our crops and natural areas:
USDA National Center for Genetic Resources Preservation
The USDA’s genebank in Colorado is one of the largest in the world. They use the term “genebanks” because they store pollen and other plant parts involved in growth and reproduction as well as seeds. They also conduct research to improve the effectiveness of gene storage methods. Their cold room contains seeds preserved in vacuum sealed envelopes, stored on shelves at -18C (0F). These seeds have a shelf life of 20 to 50 years. The cryogenic vault area stores seeds in tanks cooled with liquid nitrogen. These seeds are expected to remain viable for hundreds of years.
Millennium Seed Bank
Working in partnership with countries around the globe, the Kew Botanic Gardens in London operates this seed bank focused on the conservation of native plant species of the world. Their mission is to provide an insurance policy against the extinction of species. Their initial focus is on dryland species. Dryland habitats will become drier with climate change, pushing many of these species beyond their tolerance range. At the same time, many moderate sites will become drylands, and these species will be needed to revegetate those areas. As of June 2015, Kew had succeeded in acquiring 13% of the world’s vascular plant species.
Svalbard Global Seed Vault
Svalbard is a gift to all of us from the Norwegian people and the Bill and Melinda Gates Foundation. Buried deep in a mountain on an island in northern Norway, Svalbard’s mission is to serve as a backup storage facility for the world’s other seed vaults, protecting them from the ravages of war, storms, fire, and war. Seeds are from both the USDA and from the Vavilov Institute. The staff of the seed bank in Leningrad would have appreciated Svalbard’s mission.
By Sara Tangren, Ph. D., Sr. Agent Associate, Sustainable Horticulture and Native Plants, University of Maryland Extension, Home & Garden Information Center
Resources on Seed Saving from the University of Maryland Extension
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To keep in the spirit of Halloween, I wanted to talk about a beneficial insect with orange and black coloration. The first to come to mind is the multi-colored Asian lady beetle, Harmonia axyridis. Both the coloration and the timing (now) that they move into homes and other structures have also earned this beetle the name “Halloween beetle”.
The multi-colored Asian lady beetle is the most common lady beetle I observe in managed and natural ornamental environments. The multi-colored Asian lady beetle is native to eastern Asia and was brought to the U.S. in 1916 to control aphids in food crops. At first, they did not establish well. Around 1988, an established population was found in a natural habitat. Since then, they have adapted very well and are now found throughout the U.S.
Adults of are highly variable in color and spot pattern. Their body color ranges from a pale orange to bright red, both with and without spots, and if there are spots their number can vary. One diagnostic feature for all multicolored Asian lady beetles is a dark patch in the shape of an “M” just behind the head on the pronotum. The juvenile stages or larvae are mostly black but with two lateral orange stripes on the middle segments of their abdomen. These larvae resemble tiny, short-snouted alligators with long legs. The larvae take a week or two to develop and then transform into pupae. Within a few days, the adults will emerge from the pupal skin and resume their hunt for aphids or other prey items.
Multi-colored Asian lady beetle adults are generalist predators that have been reported to consume more than 250 aphids each day and the larvae may eat more than 1,500 during their development. Multi-colored Asian lady beetles also will consume scales, a diversity of beetles and caterpillars. They are also omnivorous and feed on nectar and pollen from plants. They are highly beneficial when it comes to reducing populations of aphids. If you don’t spray your roses (or other aphid infested plants) with pesticides, these predators really can do their job well and suppress a pest population.
Not all good beetles are good all the time. In the fall months, as the weather cools, hundreds to thousands of multi-colored Asian lady beetles begin moving indoors to hunker down for the winter. At this time, multicolored Asian lady beetles are referred to as nuisance pests. In addition to their high numbers in buildings, they also produce a defensive compound that has a bad odor which makes them a little nastier when disturbed indoors. The best method to control multi-colored Asian lady beetle as nuisance pests is to prevent them from getting in the first place. Anything that can seal openings in homes will help in their control.
By Paula Shrewsbury, Ph.D., Associate Professor and Extension Specialist, University of Maryland, Department of Entomology. This article was published originally in the University of Maryland TPM/IPM Weekly Report, October 5, 2018.
Moving into the fall season, you may see some of your pine trees turning partially brown. This is generally a natural occurrence.
Learn more about pines and other trees in the fall/winter season at our FAQ page.