Multiflora rose bushes blanket a sunny meadow, rioting over banks and into hollows with clouds of snowy blossoms. The roses climb high into the branches of trees, outlined by the bright blue sky billowing above the magnificent natural beauty.

Nothing could look less sinister. Yet sinister it is, according to a UD entomologist.

Multiflora roses have conquered the native plant species that once thrived in this natural area. The species is among many non-native plants that now dominate much of the North American countryside. Free and unchallenged by insect pests from their native homelands, the exotic plants grow wild, crowding out plants native to North American open areas and forests, upsetting the balance of nature.

Doug Tallamy, professor in the Department of Entomology and Applied Ecology, is concerned. In a recent study, he found that insects largely ignore the leaves of non-native plants, opting instead to eat the leaves of native species. But, with non-native plants choking out native growth, the insects' food supply is disappearing rapidly. At issue is the availability of insect food, a factor on which the entire food chain rests.

"Plants are at the base of the food chain," Tallamy says. "Insects feed on the plants. Other creatures feed on the insects. If insects' food supplies disappear, so do the insects and then, the creatures that eat them.

"Fewer plant food sources, fewer insects--and wildlife vanishes."

Tallamy's study found that more than 90 percent of native insects consume only the leaves of native plants, because they do not have the enzymes required to digest leaves from non-natives. While other studies have been conducted on ecological problems caused by non-native plants, the focus has been on the economics of unchecked invasion and the biological threat of displacing native plants. Tallamy quantified the effects of non-native plants on the food supply of insects, related that to the food supply of birds, which eat insects, and pointed out the consequences to ecological balance in the food chain.

He illustrates the point using the multiflora rose, a shrub introduced into North America as an ornamental plant. This rose offers excellent nesting sites for birds and provides berries for them to forage in the fall. Marketers of ornamental plants for home gardening purposely suggest the multiflora to consumers who encourage wildlife in their yards, gardens and fields.

But, this aggressively growing bush has overtaken not only home gardens but also meadows, creek banks and roadsides all over the United States, effectively choking out native plant species.

"Yes, the multiflora does provide nesting and berries for winter-feeding birds," Tallamy says, "but native birds also nest in easily available native plants. More important, when raising their young in the spring, birds depend upon a supply of insects and larvae to feed the hatchlings. When birds nest in plants insects can't eat, there are no insects for food, and future generations of birds can disappear."

Home gardeners who plant the popular butterfly bush also are mistaken in their desire to be nature-friendly, Tallamy points out. The bush is non-native to North America.

"The bush attracts butterflies to its flower nectar," he acknowledges. "But, the butterflies will not lay their eggs on the leaves, because the foliage offers no nutrition to the hatchling larvae--they can't eat it."

Green open spaces where nature appears to have taken over, Tallamy reports, might be overrun with as much as 90 percent non-native growth. "What people don't recognize," he says, "is that a green field in which native plants have been choked out is no more productive than a parking lot when it comes to providing food for insects, birds and other animals.

"Planting a native species, such as viburnum, milkweed, Joe Pye weed or purple cone flower, for every butterfly bush or multiflora rose will really help nature."

Tallamy is optimistic that the data he has collected will attract the attention of homeowners who can influence the home garden marketplace.

"I hope the scientific evidence gathered in the study will help spur people into action," he says. "Imagine the future impact on insect and animal populations, and on our natural heritage, if homeowners replaced the non-native ornamental plants on their property with plant species historically native to the area--and friendly to the ecosystem."

--Marianne Kirby Rhodes

A taste test for insects

Here are some examples of non-native plants, which most insects are unable to eat, and native plants, on which they prefer to feed. Doug Tallamy, professor of entomology and applied ecology, says the encroachment of non-native plants could decrease the insect population and, therefore, endanger the birds and other animals that feed on them.

Non-native ornamental plants Multiflora rose Oriental bittersweet Japanese honeysuckle Autumn olive Mile-a-minute weed Garlic mustard Norway maple Ox-eye daisy Red clover

Native ornamental plants Viburnum Hickory Oak Black walnut Black willow Elderberry Goldenrod Black cherry Red maple