Urban tree arrangement and health influence infestation by invasive leaf-mining and sap-sucking insects

Abstract

Urban trees play a vital role in supporting biodiversity, enhancing human well-being, and promoting climate resilience. However, they are increasingly threatened by invasive insect pests. These pests belong to different feeding guilds, such as leaf-miners and sap-suckers, which may respond differently to the tree spatial arrangement and health of trees. Understanding how specific strategies of these pest groups interact with tree spatial arrangement, tree health, tree size, levels of defoliation, and the proportion of neighboring conspecific trees is crucial for explaining how infestations develop in urban areas. This study investigated how these factors influence infestations by three invasive pests: the horse-chestnut leaf miner ( Cameraria ohridella ), the plane leaf miner ( Phyllonorycter platani ), and the sycamore lace bug ( Corythucha ciliata ). Results Infestation intensity increased across all species as summer progressed ( p < 0.001 for all species). C. ohridella reached the highest levels on solitary horse chestnuts, while P. platani was more abundant on plane trees growing in stands or groups. Proximity to conspecific trees reduced C. ohridella infestation, whereas healthier plane trees exhibited lower C. ciliata abundance. Tree size had no consistent effect, and defoliation did not reduce infestation in any species, despite significantly higher defoliation in horse chestnut compared to plane trees ( p = 0.002). Leaf-mining and sap-sucking guilds differed in their spatial responses. Conclusions Fine-scale tree spatial arrangement and host condition are associated with variation in invasive pest dynamics in urban environments. Guild-specific differences in spatial responses and the finding that defoliation did not reduce infestation highlight the importance of local tree context for understanding infestation patterns of multivoltine pests. These insights may support the design of more resilient urban plantings, particularly through strategic arrangement of host trees and maintaining host vitality.