Insect hipsters hang out in the hot spots of the city. Scale insects (Parthenolecanium quercifex) aren't looking for the hippest club, instead they seek a tasty tree to eat.
Scale insects were 13 times more abundant on oaks in hotter parts of Raleigh, North Carolina, according to research published in PLOS ONE.
Botanists and entomologists already knew that insect pests tended to be more abundant in cities than in surrounding suburbs and rural areas. Scientists hypothesized that urban ecosystems may have lower levels of insect predators or that trees in the city are more stressed and susceptible to attack, but these factors didn't entirely explain the phenomenon. It seems the "urban heat island" effect may be another reason insects dig the scene in the city's hot spots.
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The concrete, asphalt and brick of a modern city heat up faster and retain more heat than a forest or field. Tall buildings can block cooling breezes. Plus, human activities in the city contribute to the heat. Hence, cities tend to form pockets of heat, or "heat islands," compared to surrounding open areas.
"Urban warming can lead to higher insect pest abundance, a result of pest acclimation or adaptation to higher temperatures," said study author Emily Meineke from North Carolina State University in a press release.
Meineke and her co-authors suggested that the outbreaks of bugs in the city may be a warning for forests in a warming world.
"Since urban warming is similar in magnitude to global warming predicted in the next 50 years, pest abundance on city trees may foreshadow widespread outbreaks as natural forests also grow warmer," the authors wrote in PLOS ONE.
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Bad news for trees may be good news for ants. Some species of ants tend scale insects as if they were livestock. The ants guard the scale insects and collect their secretions, called honeydew. The ants then feed upon the scale insects' honeydew, like a dairy farmer drinking milk.
IMAGE: Ants tending scale insects for honeydew (Alex Wild, Wikimedia Commons)