CABI scientists have led an 11-year study which shows how the invasive harlequin ladybird (Harmonia axyridis) caused the severe decline of the two-spotted ladybird (Adalia bipunctata) on broadleaved trees and shrubs in northern Switzerland.
Lead author Dr Marc Kenis, Head of Risk Analysis and Invasion Ecology based at CABI’s Swiss Centre in Delémont, of the research – published in the journal Insects – said the two-spotted ladybird was the most abundant ladybird at the 40 sites surveyed before the harlequin ladybird took hold between 2006 and 2017.
The scientists discovered that the harlequin ladybird – which is a predator native to Central and East Asia and whose presence was confirmed in Switzerland in 2004 – quickly dominated the broadleaved hedges representing 60-80% of all specimens collected in this habitat.
However, while the harlequin ladybird was the second most abundant species in pine stands it was not abundant in meadows and spruce stands. Furthermore, the total number of ladybirds feeding on aphids did not decline during the study period – suggesting that the arrival of the harlequin ladybird did not affect the predation pressure on aphids.
The harlequin ladybird is considered a human nuisance when it aggregates in buildings in autumn and can taint wine when harvested and crushed with grapes. Of most concern, however, is its impact on biodiversity.
Due to its predatory and competitive abilities, H. axyridis may affect many native species, including non-pest aphids and aphidophagous insects. In particular, native ladybirds may suffer from competition for resources and intra-guild predation (IGP) on larvae and eggs.