Response of the soft scale insect Parthenolecanium corni and its natural enemies on honeylocust trees to urban conditions

[Display omitted] •Impervious surface cover around street trees can increase tree canopy temperature.•Fitness of soft scale insects is increased more by impervious surface in hot than cool sites.•Absence of a positive numerical response of parasitoids in hot sites suggests scale outbreaks are driven by bottom up factors.•Presence of a positive numerical response of parasitoids to low host densities suggest potential for biological control.•Elevated temperatures may increase pest abundances in ways that are not mitigated by natural enemies. Urban habitats can alter tree physiology in ways that make trees more susceptible to insect pests. We examined how urban conditions (e.g., impervious surfaces and warming) affected the soft scale insect, European fruit lecanium, Parthenolecanium corni Bouché (Hemiptera: Coccidae) and the health of thornless honeylocust trees (Gleditsia tricanthos L. var. inermis) in Indianapolis, Indiana, USA. Hot and cool study sites were selected based on surface air temperatures obtained from thermal LANDSAT-8 images overlaid against a map of honeylocust tree locations. Based on temperature probe data, study trees located in hot sites had mean average daily temperatures up to 1.56 °C and 1.79 °C warmer than cool sites in 2019 and 2020, respectively. We hypothesized that abundance and fecundity of scale insects would be higher on trees in hot sites and those surrounded by more impervious surface cover within a 20 m radius. Although our data supported these hypotheses, impervious surface cover predicted more of the variation in abundance and fecundity of scale insects in hot sites compared to cool sites. Rates of parasitism were not affected by impervious surface cover or whether the site was from a hot or cool location. However, we found strong density dependence in parasitism of scale insects in both hot and cool sites when scale densities were at or below the levels present in cool sites. This suggests that lower densities of scale insects were associated with a positive numerical response of parasitoids, a necessary prerequisite for population regulation by top-down effects. In contrast, this numerical response was lacking at the higher densities of scales found on trees located in hot sites where, presumably bottom-up factors like water-stress increased the fecundity of scale insects. These findings add to a growing body of evidence linking rising global temperatures with increased pest abundance in ways that cannot be mitigated by