1. Harmonia axyridis (Coleoptera: Coccinellidae) is an invasive non-native ladybird in Europe, where it was introduced as a biological control agent of aphids and coccids.
2. This study assesses changes to ladybird species assemblages, in arboreal habitats, over a 3-year period encompassing the invasion phase of H. axyridis in eastern England. The effects of H. axyridis and other factors (weather and prey availability) on native ladybirds are assessed.
3. Harmonia axyridis increased from 0.1% to 40% of total ladybirds sampled, whilst native aphidophagous species declined from 84% to 41% of total ladybirds. The actual number of native aphidophagous ladybirds per survey decreased from a mean of 19.7 in year 1, to 10.2 in year 3.
4. Three ladybird species in particular experienced declines: Adalia bipunctata, Coccinella septempunctata, and Propylea quattuordecimpunctata. Harmonia axyridis was the most abundant species by the end of the study.
5. The decline in native aphidophagous ladybirds could be attributed to competition for prey and intraguild predation of eggs, larvae, and pupae by H. axyridis. Physiological and behavioural traits of H. axyridis are likely to confer an advantage over native ladybird species.