As alien plants grow, biodiversity suffers

Chris Philips says he tries to live by Mahatma Gandhi’s words: “You must be the change you want to see in this world.”

Philips, a graduate student in entomology and wildlife ecology, was recalling that sentiment one unseasonably chilly afternoon last spring as he methodically planted a Norway maple next to a red maple, an English blue holly next to American holly, and a Korean rhododendron next to a pink azalea. A few months later, in the sticky heat of summer, Gandhi’s words still seemed to run through Philips’ head as he pushed a lawn mower in between the rows of shrubs and trees.

Despite his diligent maintenance work, this garden wouldn’t win any prizes for aesthetics. The 125-by-50-foot plot, tucked behind Delaware Stadium and bordered by the UD Woods, is strictly utilitarian in design.

Philips’ gardening efforts focus not on what the casual observer sees but on what can be detected upon closer examination—insects. The garden is all about the insects flying about, landing on and, most importantly, feeding on these native and non-native plants that are growing side by side. The garden is the cornerstone of Philips’ research project, “The Impact of Alien Plants on Native Insect Herbivores,” which is supported by a four-year grant from the National Science Foundation.

Philips, who is conducting this research in conjunction with Doug Tallamy, professor and chairperson of the Department of Entomology and Wildlife Ecology, wants to find out if non-native plants support as many native insects as do plants in the same genus that are native to Delaware. To conduct his research, he periodically collects samples of insects in the plot.

The sampling technique is simple but effective. Using a modified leaf blower fitted with a nylon mesh bag, Philips sucks insects off the alien Norway maple, for example, and compares this cache with what he collects off the native red maple.

The analysis focuses on insect biomass—the sheer number of insects on the native plants versus the non-natives—as well as by identification of insect species. Species are categorized by whether they are generalists, which eat many different plants, or specialists, which eat only one species of plant or several closely related plants. The researchers want to see if non-native plants affect these two categories of insects differently.

All the detailed analysis and identification occurs in Tallamy’s laboratory and can take months to accomplish. But Philips says he finds the work deeply rewarding.

“Insects consistently get a bad rap,” he says. “But they play a crucial role in maintaining the integrity of the ecosystem.

“I first learned about Doug’s various projects at a professional conference, and I knew then that UD was where I belonged. I wanted to play a part in research that helps us better understand the complex relationship between insects and plants. Hopefully, the knowledge we gain will prove useful in biodiversity conservation efforts.”

Do alien plants reduce the native insect population? That’s the $64,000 question, Tallamy says, adding that preliminary research findings do suggest that alien plant species reduce the population of native insect herbivores.

To those who have never appreciated bugs, that may sound like a good thing. Plant a non-native Kousa dogwood and be rewarded with fewer pesky insects than you would if you planted a native variety, such as an alternate-leaf dogwood.

Tallamy stresses, however, that all insects are beneficial (even if they aren’t, strictly speaking, beneficial insects). As defined by entomologists, beneficial insects are pollinators, decomposers, predators and parasites whose actions are useful to humankind. Think of the native bee pollinating blueberry bushes, the ladybug beetle that eats up the aphid pest and the preying mantis that gobbles flies, mosquitoes and anything else it can capture.

But beyond the well-recognized advantages of the beneficial insects, Tallamy says that all insects. even those that most people aren’t crazy about, are important for preserving biodiversity.

“A diverse ecosystem is critically important,” he says. “All species, including insects, have a critical role to play in the productivity of an ecosystem.”

These days, in Delaware and around the world, naturally biodiverse habitats are rapidly disappearing. They’re often replaced by suburban yards that are planted with 80-90 percent non-native species.

“The suburban/urban landscape is now the dominant ‘ecosystem,’” Tallamy says. “The need to understand the ability of introduced plants to support native fauna has never been more urgent.”

—Margo McDonough, AS ’86, ’95M