Urban Warming Drives Insect Pest Abundance on Street Trees

Abstract

Cities profoundly alter biological communities, favoring some species over others, though the mechanisms that govern these changes are largely unknown. Herbivorous arthropod pests are often more abundant in urban than in rural areas, and urban outbreaks have been attributed to reduced control by predators and parasitoids and to increased susceptibility of stressed urban plants. These hypotheses, however, leave many outbreaks unexplained and fail to predict variation in pest abundance within cities. Here we show that the abundance of a common insect pest is positively related to temperature even when controlling for other habitat characteristics. The scale insect Parthenolecanium quercifex was 13 times more abundant on willow oak trees in the hottest parts of Raleigh, NC, in the southeastern United States, than in cooler areas, though parasitism rates were similar. We further separated the effects of heat from those of natural enemies and plant quality in a greenhouse reciprocal transplant experiment. P. quercifex collected from hot urban trees became more abundant in hot greenhouses than in cool greenhouses, whereas the abundance of P. quercifex collected from cooler urban trees remained low in hot and cool greenhouses. Parthenolecanium quercifex living in urban hot spots succeed with warming, and they do so because some demes have either acclimatized or adapted to high temperatures. Our results provide the first evidence that heat can be a key driver of insect pest outbreaks on urban trees. 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.

Dragonflies and damselflies (Odonata) in urban ecosystems: A review

“…Most odonates are likely to tolerate such warm conditions due to their tropical evolutionary origin (Pritchard & Leggott, 1987), although thermal stress can be lethal if the temperatures exceed upper tolerance thresholds. In fact, the UHI may facilitate dispersal of odonates, as has been found in scale insects (Meineke et al, 2013) and mosquitoes (Araujo et al, 2015). It has been suggested that cities in temperate regions may benefi t from the increased temperature, particularly during winter, although the UHI can also increase thermal and drought stress in tropical, subtropical and desert cities (Shochat et al, 2006).…”

Early pest development and loss of biological control are associated with urban warming

“…We harvested P. quercifex egg sacs from sites used in Prediction 1 along with three additional hot sites and two additional cold sites from our original study [4] to add replicates, for a total of 10 hot and 10 cold sites. At each site, we collected 40 dead females on 23 -24 April 2012, before P. quercifex eggs hatched.…”

“…In a previous study, we found that the scale insect Parthenolecanium quercifex (Hemiptera: Coccidae) is 12 times more abundant on trees in the warmest urban habitats [4]. Female P. quercifex are attacked by several hymenopteran parasitoids that kill them or reduce their fecundity.…”

Urban warming reduces aboveground carbon storage

“…For example, urban warming increases densities of two native scale insect species that survive better [23] and produce more eggs [24,25] at hotter urban sites.…”