Host plant identity and condition shape phytophagous insect communities on urban maple (Acer spp.) trees

Dávid Korányi,Viktor Markó

doi:10.1007/s11829-022-09887-z

Abstract

By mitigating the negative effects of urbanization, urban trees contribute significantly to the well-being of urban citizens. However, trees themselves are also exposed to urban stress that can influence tree condition and tree-herbivore interactions. Maple species (Acer spp.) are among the most commonly planted trees in urban areas throughout North America and Europe. Among these species, field, sycamore, and Norway maple are native to Europe, but tolerate environmental stress to varying degrees. Here, we compared the phytophagous insect communities in the canopy of these tree species in the city of Budapest, Hungary. We also examined the stress level [expressed as peroxidase (POD) enzyme activity], and physiological condition (expressed as degree of leaf necrosis and leaf fall) of the maple trees, and their relationship to herbivore abundance. We observed higher total abundance of phytophagous insects on field and sycamore maple compared to Norway maple. Most herbivorous species were associated with field maple, sycamore had the highest aphid densities, and Norway maple harbored the least specific phytophagous insect community. Field maple trees were in the best condition while Norway maple trees in the worst condition, i.e., with the highest proportion of necrotic leaf surface area. The super-abundant planthopper species, Metcalfa pruinosa positively affected the POD activity of trees, but did not influence their condition. On the contrary, M. pruinosa abundance was driven by tree condition, with higher numbers on healthier trees. Our findings suggest that the abundance of phytophagous insects in the canopy of maple trees is highly determined by tree condition, and in this study field maple had the highest and Norway maple the lowest tolerance for urban stress.

Highlights

Urban areas represent a relatively small proportion of the total Earth surface, the urban land-cover continues to grow and is predicted to increase by 1.2 million km2 in the first 30 years of the 21st century (Seto et al 2012)
The psyllid R. aceris was associated with field maple, while we found no difference between the abundances of Cacopsylla pulchella (Low) on the three maple species
We observed a significant increase in POD activity in maple trees with increasing numbers of M. pruinosa individuals, while the abundant phytophagous groups had no effect on this variable (Table 1)

Summary

Introduction

Urban areas represent a relatively small proportion of the total Earth surface, the urban land-cover continues to grow and is predicted to increase by 1.2 million km in the first 30 years of the 21st century (Seto et al 2012). Trees contribute to the mitigation of abiotic environmental changes associated with urbanization, have important role in providing a livable environment for humans. Urban trees reduce air temperature by absorbing solar radiation through evapotranspiration and reduce surface temperatures via shading (Rahman et al 2017). Trees remove significant amounts of air pollutants originating from traffic and industrial activity, by absorption and by dry deposition on plant surfaces (Nowak et al 2006). Trees are highly exposed to different factors associated with urbanization, including heat stress, increased emissions, low air humidity and periods of critical

Methods

Results

Discussion

Conclusion