Harmonia axyridis implicated in native European ladybird declines

Abstract

Rates of global extinction are accelerating and show no sign of slowing (Millenium Ecosystem Assessment, 2005). Invasive alien species (IAS) are recognised as major drivers of biodiversity loss (Winter et al., 2009). IAS afford a unique opportunity to accurately assess threats to biodiversity because the time at which an IAS arrives within an ecosystem is often known, unlike other drivers of change. However, few causal relationships between IAS and species declines have been documented. We used data collated through extensive citizen-driven field surveys in Belgium and Britain spanning decades, as well as intensive monitoring by scientists in Belgium, Britain and Switzerland. The fine-scale data collection, replicated in time (over decades and including detailed observations before and after the arrival of an IAS) and with extensive coverage in three European countries, combined with powerful modern mixed-modelling (statistical) techniques, provided a uniquely rigorous test of the impacts of an IAS on biodiversity. We report rapid, dramatic and ongoing declines in the distribution of formerly common and widespread native ladybirds in Belgium and Britain following the arrival of Harmonia axyridis (Coleoptera: Coccinellidae), a globally rapidly expanding IAS (Roy et al., 2012). For example, the two-spot ladybird, Adalia bipunctata (Coleoptera: Coccinellidae), declined in both Belgium and Britain over five years after the arrival of H. axyridis