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Simple Summary: Harmonia axyridis (Coleoptera: Coccinellidae) is a widespread invasive ladybird. In this study, we determine its occurrence and expansion in urban areas of the Iberian Peninsula after 2014. We also define the aphidophagous ladybird species complex in urban areas of the northeastern Iberian Peninsula and track any changes between 2015 and 2021. The expansion of the species mainly occurred in Catalonia (northeast Iberian Peninsula), where spring and summer populations on trees and shrubs and overwintering aggregations were recorded. The records of H. axyridis populations allow us to distinguish between two areas: one that has already been invaded and another that has not yet been invaded. The relative abundance of the ladybird species in each area is determined on a yearly basis. In the invaded area, H. axyridis became dominant two years after its detection, replacing Adalia bipunctata. This change in species prevalence is more pronounced in trees highly infested with aphids. In the not yet invaded area, changes in species dominance also occurred, and A. bipunctata replaced Oenopia conglobata from 2020 onwards. The yearly release of this ladybird in urban green areas for aphid control purposes could explain this shift. This study defines the current situation of H. axyridis in the Iberian Peninsula, and determines the main changes in ladybird species assemblages during the last few years. In the Western Palearctic region, Harmonia axyridis (Coleoptera: Coccinellidae) is mainly established in urban areas. In this study, we update its occurrence in urban areas of the Iberian Peninsula and determine its expansion after 2014. Changes in the ladybird species assemblage are also evaluated. We compile information about the records of H. axyridis in Spain from 2015 to 2021. In addition, we sample different locations to determine the relative abundances of the species composing the aphidophagous ladybird complex. The expansion of H. axyridis mainly occurred in Catalonia (Iberian Peninsula), where it is possible to identify two clear areas: one that has already been invaded and another that has not yet been invaded. Harmonia axyridis became the dominant species in the invaded area two years after it was first identified. This dominance is clearly shown on Liriodendron tulipifera and Tilia platyphyllos, where it accounted for more than 75% of the total collected individuals in the last year of the study. In the not-yet invaded area, Adalia bipunctata overcame Oenopia conglobata and became the prevalent species from 2020 onwards, likely due to its regular releases for aphid biocontrol. This study reveals that changes in ladybird species assemblages may not only be caused by invasive species, but also by biological control practices. [ABSTRACT FROM AUTHOR]

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