Warming and drought combine to increase pest insect fitness on urban trees.

Adam G Dale,Steven D Frank,Daniel Doucet

doi:10.1371/journal.pone.0173844

Adam G Dale, Steven D Frank + Show 1 more

Open Access

https://doi.org/10.1371/journal.pone.0173844

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Journal: PloS one	Publication Date: Mar 9, 2017
Citations: 118	License type: CC BY 4.0

Affiliation: University of Florida, North Carolina State University

Abstract

Urban habitats are characterized by impervious surfaces, which increase temperatures and reduce water availability to plants. The effects of these conditions on herbivorous insects are not well understood, but may provide insight into future conditions. Three primary hypotheses have been proposed to explain why multiple herbivorous arthropods are more abundant and damaging in cities, and support has been found for each. First, less complex vegetation may reduce biological control of pests. Second, plant stress can increase plant quality for pests. And third, urban warming can directly increase pest fitness and abundance. These hypotheses are not mutually exclusive, and the effects of temperature and plant stress are particularly related. Thus, we test the hypothesis that urban warming and drought stress combine to increase the fitness and abundance of the scale insect, Melanaspis tenebricosa, an urban tree pest that is more abundant in urban than rural areas of the southeastern U.S. We did this by manipulating drought stress across an existing mosaic of urban warming. We found support for the additive effect of temperature and drought stress such that female embryo production and body size increased with temperature and was greater on drought-stressed than watered trees. This study provides further evidence that drivers of pest insect outbreaks act in concert, rather than independently, and calls for more research that manipulates multiple abiotic factors related to urbanization and climate change to predict their effects on ecological interactions. As cities expand and the climate changes, warmer temperatures and drought conditions may become more widespread in the native range of this pest. These changes have direct physiological benefits for M. tenebricosa, and potentially other pests, that may increase their fitness and abundance in urban and natural forests.

Highlights

Urban forests are often more heavily infested with herbivorous arthropod pests than surrounding rural areas [1]
Xylem vulnerability curves conducted by Johnson et al [42] suggest that A. rubrum is moderately drought tolerant and can withstand as low as -3.9 MPa of xylem negative pressure before embolism occurs in 50% of vessels, indicative of severe drought stress
We found that the warmest, unwatered A. rubrum street trees surpassed -3.9 MPa during midday water potential measurements (Fig 2), suggesting that damaging levels of drought stress are occurring in Raleigh’s A. rubrum street trees that do not receive irrigation

Summary

Introduction

Urban forests are often more heavily infested with herbivorous arthropod pests than surrounding rural areas [1]. One well supported hypothesis suggests that features of urban landscapes support fewer natural enemies, creating enemy-free space that allows herbivores to proliferate [2,3,4]. Urban warming has been shown to play a major role and may outweigh factors associated with. Urban warming and drought increase pest fitness the understanding that the United States Government is authorized to reproduce and distribute reprints for governmental purposes. Funding for this work was provided by a Southeast Climate Science Center graduate fellowship awarded to Adam Dale. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

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