Sarah Parsons, a Ph.D. candidate in entomology at North Carolina State University, visits one of her crape myrtle study trees. The tree is surrounded by minimal local vegetation, as is common of many trees in the urban environment. According to Parsons’ findings, this would be a tree where one would expect to find fewer Orius insidiosus, a predator of the crapemyrtle aphid (Tinocallis kahawaluokalani). Orius numbers increase with more dense vegetation distributed locally around the tree.

By Sarah Parsons

“Is the tree okay?” An undergraduate, no more than 19, looked up at me with a concerned expression. His freckles scrunched together on his worried brow. “Yes,” I said, reassuringly. “The tree will be just fine.” I then launched into my usual elevator speech about what I was doing. By the end of the 30-second interaction, his freckles returned to their natural random distribution on his face, uncollecting from the clumpiness around his brow furrows, and he turned to continue on his way. I’m sure his calculus class would cause his freckles to clump again, but at least for now he could let his freckles rest, unencumbered by the worries of the world.

Sarah Parsons

Urban ecologists receive lots of questions in the “field.” People make up an integral part of the ecosystems we study. They help shape and create the ecosystems. They manage them, sometimes to our dismay. And yet sometimes they show care for them, like the curious undergraduate who asked me about the fate of my study tree. I receive all manner of questions and facial expressions from people passing by. I elicit the strongest responses from city dwellers when I do beat sampling, a process that quite literally requires beating a tree canopy with a stick and collecting the arthropods that fall on a sheet placed underneath. I know I look strange, like a woman who has lost her mind and is taking out her life’s disappointments on an innocent tree. Sometimes I wish I could quantify how many people passing by think I have “lost my marbles.” Maybe one day I’ll do a survey.

My research is conducted on a system that would not exist without human intervention. I study a non-native specialist aphid, the crapemyrtle aphid (Tinocallis kahawaluokalani), which lives on non-native crape myrtles in Raleigh. My research looks at how the urban habitat around crape myrtles affects aphids and their arthropod predators. Unfortunately, urban trees are often stressed by pests, hot temperatures, and lack of water. In keeping with previous work, I have found that crapemyrtle aphids increase on trees surrounded by higher amounts of impervious surface (e.g., pavement and buildings). However, encouragingly I have also found that one predator of aphids, Orius insidiosus, does well in urban environments, particularly on those trees surrounded by more vegetation. Next steps of my research will look to establish vegetation “thresholds” that landscape designers can use when designing landscapes around street trees to support large populations of O. insidiosus and reduce pesticide use to control tree pests.

Crape myrtles are among the most common urban trees in the Southeast U.S., and crapemyrtle aphids (Tinnocallis kahawaluokalani), pictured here, are their primary pest. Crapemyrtle aphids are specialist herbivores that eat plant phloem, and their primary natural enemies include generalist predators, such as lady beetles, Orius insidiosus, and lacewings. (Photo credit: Jim Baker, North Carolina State University, Bugwood.org)

Sarah Parsons’ research has shown that Orius, a predator of crapemyrtle aphids, thrives in city environments on crape myrtles surrounded by dense vegetation distributed locally around the tree. (Photo credit: Melinda Gibbs, NC State University)

As I watched the freckled faced undergrad walk away that day, I was hopeful. Some people care about the fate of life in our urban spaces, and some people, like me, care enough to study them. Our cities sometimes are not great for the lives they house, but I have hope they will get better. Together, by learning about the mechanisms that drive urban ecosystems, we can better design our cities so that they are healthier for both people and our planet.

For more information about my work and the work of other entomologists in urban insect ecology at NC State visit http://ecoipm.org

Sarah Parsons is Ph.D. candidate in entomology at North Carolina State University. Email: separson@ncsu.edu