UD grad student studies insect damage to plants
Erin Reed, right, works with Sarah Rusk in the study of insect damage to plants.
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10:03 a.m., June 22, 2009----On a recent morning, Erin Reed sat in a stranger's backyard in Chester County, Pa., and counted bugs. Specifically, the number of bagworms that could be found on a black cherry tree.

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Suburban yards, as well as laboratories and field plots, can be the setting for university research. Reed's bug counting is part of a two-year study that may ultimately contribute to the greater use of native plants in the landscape.

Which would be a very good thing in the eyes of Reed, a University of Delaware graduate student, and in the eyes of her research adviser, Doug Tallamy, chairperson of the Department of Entomology and Wildlife Ecology in the College of Agriculture and Natural Resources.

Native plants serve as food and habitat to attract and support a variety of local wildlife. In contrast, non-native plants can alter, degrade, and deplete nutrients, water, and organisms within the soil and cause erosion, degrading aquatic and terrestrial habitats, according to Tallamy, the author of Bringing Nature Home: How Native Plants Sustain Wildlife in Our Gardens. This 2007 release was met with critical acclaim in The New York Times and elsewhere.

So why do homeowners continue to plant non-natives?

“We think some people have the impression that native plants suffer a lot of insect damage and that non-natives are more pest- and disease-resistant,” says Reed, who became interested in native plant research as a UD undergraduate studet. After receiving her wildlife conservation degree in 2007 she decided to pursue a master's in wildlife ecology.

“People also think that non-natives are hardier than natives, more drought tolerant, and have the ability to provide quality food for wildlife,” adds Reed.

But the research that this 24-year-old Berks County, Pa., native is currently conducting in area backyards may refute at least one of these perceptions -- that native plants sustain more insect damage than non-native plants.

Tallamy, in conjunction with University of Maryland researcher Paula Shrewsbury, already has conducted studies in research plots that indicate that native plants sustain no more insect damage than non-native plants.

That's because many insects are attracted to native plants -- insects that go on to eat other insects and thus control large pest outbreaks, explains Tallamy.

Not as many insects are attracted to non-native plants, which means that there aren't as many natural controls available when non-native plants do experience a pest outbreak.

“Although somewhat counterintuitive, the notion that one must maintain 'pests' in order to control 'pests' is well-documented,” says Tallamy.

“The central tenet of conservation biological control is that low densities of plant-eating insects must persist in a planting to attract and retain natural enemies,” says Tallamy. “When this is the case, predators -- everything from birds to predatory insects -- and parasites are already present to prevent or suppress outbreaks when a potential pest enters the planting.”

Reed's work takes Tallamy's research -- which was conducted in controlled, replicated plots -- a step further by testing conditions in suburbia itself. She has been tallying insects at six area properties landscaped exclusively with native plants.

And she also has been tallying insects at six properties that are a match for each of these properties -- a property of the same size in the same neighborhood with the same plant diversity and abundance but that is traditionally landscaped with a mix of both native and alien plants.

Besides counting bagworms on black cherries, she is looking at three other common native pest insects on their native host plants -- cabbage looper on cabbage plants, hornworms on tomato plants and white-marked tussock moths on black cherries.

In addition to determining if natives can suppress pest abundance in suburban settings, Reed is measuring how insect damage inflicted on natives compares to damage sustained by plants in gardens comprised mostly of aliens.

“Last year's data indicates that native plants received no more insect damage than non-native plants,” says Reed. “Both natives and non-natives had about 4 percent defoliation, well below the 10 percent damage threshold of what is acceptable to most homeowners.”

Reed still has a summer's worth of data to collect and then a semester to crunch numbers before writing up her final research report. She expects to graduate in January and after that would like to work in an educational role to promote native plants.

Tallamy has produced a list of what he believes are the 20 most valuable native plants for supporting biodiversity in the Mid-Atlantic.

Article by Margo McDonough
Photo by Danielle Quigley