John Metcalfe was CityLab’s Bay Area bureau chief, covering climate change and the science of cities.
The hotter neighborhoods of Raleigh are awash in scale insects, an ominous indicator of how bug populations might swell in a globally warmer world.
We often think of cities as dampening zones for wildlife, with bustling human activity and inhospitable concrete surfaces keeping many critters at a distance. But in reality the opposite might be the case, at least for insects: They seem to love basking in the toasty air of the urban heat island.
That's the take-away of a new study out of Raleigh conducted by Emily Meineke at North Carolina State University and entomology enthusiasts around the state. Meineke and friends wanted to know if urban pest outbreaks had anything to do with the warm air wafting off of cities. So they set their sights on Parthenolecanium quercifex, or the oak lecanium, a type of scale insect whose extreme slothfulness makes it the Al Bundy of the bug world.
Many people have probably seen the creatures without even realizing they're there. They look like small, unmoving bumps, coated in wax or cottony fluff, sucking plant juices and pooping out sweet nectar that's sometimes farmed by opportunistic ants. Meineke's posse tromped through Raleigh examining street oak trees to establish where the arthropods lived. They then compared population numbers between cooler and warmer neighborhoods while eliminating factors like the presence of natural predators. Their conclusion: The insects really prefer to hang out in the warmer 'hoods, with infestations as much as 13 times larger than those in chillier nabes.
This is a thermal map they made showing scale-insect populations scattered throughout the warmer areas of Raleigh. The black dots represent bug abundance per 30.5 centimeters of plant stem:
The study is kind of a groundbreaking effort in the research niche where insects, cities and weather intersect. As the scientists note:
Urbanization of an area changes the species that dwell in it. Previous studies have analyzed these effects in terms of loss of resources or changes to habitat, but this is the first research to focus on the effects of "heat islands" created in cities. Meineke explains that, "Urban warming can lead to higher insect pest abundance, a result of pest acclimation or adaptation to higher temperatures."
The study concludes that since current urban warming is similar in magnitude to the higher temperatures predicted by global warming in the next fifty years, their results may indicate potential changes in pest abundance as natural forests also grow warmer.
That doesn't sound too bad until you start wondering if the heat island influences the multitudes of other pests – mosquitoes, obviously, and <shudder> bed bugs. Get on that follow-up study immediately, guys. (Here's the full paper in PLOS ONE.)
Top photo of a scale insect in Bangalore, India, courtesy of Vijay Cavale on Wikipedia.