Urban environments have species-specific associations with invasive insect herbivores

Urban areas are expanding rapidly, with the majority of the global and US
population inhabiting them. Urban forests are critically important for
providing ecosystem services to the growing urban populace, but their
health is threatened by invasive insects. Insect density and damage are
highly variable in different sites across urban landscapes, such that
trees in some sites experience outbreaks and are severely damaged while
others are relatively unaffected. To protect urban forests against damage
from invasive insects and support future delivery of ecosystem services,
we must first understand the factors that affect insect density and damage
to their hosts across urban landscapes. This study explores how a variety
of environmental factors that vary across urban habitats influence density
of invasive insects. Specifically, we evaluate how vegetational
complexity, distance to buildings, impervious surface, canopy temperature,
host availability, and density of co-occurring herbivores impact three
invasive pests of elm trees: the elm leaf beetle (Xanthogaleruca luteola),
the elm flea weevil (Orchestes steppensis), and the elm leafminer (Fenusa
ulmi). Except for building distance, all environmental factors were
associated with density of at least one pest species. Furthermore, insect
responses to these factors were species-specific, with direction and
strength of associations influenced by insect life history. These findings
can be used to inform future urban pest management and tree care efforts,
making urban forests more resilient in an era where globalization and
climate change make them particularly vulnerable to attack. Keywords:
urban forest, invasive species, impervious surface, temperature, species
interactions.