Tree diversity and density affect damage caused by the invasive pest Cameraria ohridella in urban areas

Abstract

Invasive, non-native invasive pests pose a growing threat to urban trees and the services they provide to urban residents. With the reluctance to use chemical insecticides in cities, environmentally friendly methods of pest management are needed. Tree diversity is known to affect insect herbivory in forest, with higher tree species diversity leading to lower level of damage. However, the validity of those findings for a non-native insect in an urban environment remains to be demonstrated.We monitored 54 horse chestnut trees attacked by the invasive horse chestnut leafminer Cameraria ohridella in the city of Bordeaux, France. We analyzed the effects of neighboring tree diversity and density on the abundance, damage and parasitism rate of these leafminers.We showed that the abundance and damage of C. ohridella significantly increased with higher local tree canopy cover. We found that the parasitism rate of C. ohridella increased with the species diversity of neighboring trees. However, this increase in parasitism rate was not associated with a decrease in leaf area damaged.Our results pave the way for the management of exotic insect pests in cities based on the manipulation of spatial distribution and species diversity of urban trees.

An Urban Forest Diversification Software to Improve Resilience to Global Change

“…Paquette et al (2021) suggested that planting species from different functional groups improves functional diversity and thus increases urban forest resilience, because tree species with different traits will have different responses to threats. Urban forests face and will continue to face unexpected stressors associated with global change (e.g., climate change, novel pests or pathogens), such as the increasing frequency of drought events, the extension of urban heat islands, and the invasion of emerald ash borer, Dutch elm disease, and horse chestnut leafminer, which may lead to large losses of trees and their associated benefits (Raupp et al 2006;Ordóñez and Duinker 2015;Lovett et al 2016;Hudgins et al 2022;Stemmelen et al 2022). The particular problem encountered by city managers is the high uncertainty about what extreme weather events (e.g., wind storms, heat stress, ice), exotic insects, or diseases will hit next (Foran et al 2015), reinforcing the importance of increasing diversity to be better prepared for any eventuality.…”