Rapid spread of Harmonia axyridis in Chile and its effects on local coccinellid biodiversity

Aim: Biological invasions are one of the major threats to biodiversity. Usually highly disturbed anthropogenic habitats favour invasion by alien species such as the coccinellid Harmonia axyridis. The spread and impact of this species has been documented in Europe and North America, but no information exists for South America. The aims of this study were to: (1) document the process of invasion of H. axyridis in Chile, (2) compare the abundance of H. axyridis in different habitats with varying degrees of disturbance and (3) assess change in the coccinellid assemblages in alfalfa fields over the 6 years following invasion. Location: Chile. Methods: The spread of H. axyridis was estimated using information from citizen scientists alongside records from the National Pest Surveillance System. The abundance of H. axyridis in different habitat types and of all coccinellids in alfalfa fields was assessed using yellow sticky traps. In alfalfa, the variations in species richness, Shannon and Simpson diversity and equitability indices through time were compared. Results: Harmonia axyridis has rapidly increased in distribution: there have been 1875 records along 2863 km up to 2015 following the first observation in 2008 from Central Chile. The records span from sea level to 3200 m a.s.l. in the Andes. It has spread at an average rate of 184.8 km per year, preferentially colonizing disturbed habitats, but also invading native habitats. In alfalfa, it is particularly abundant and has become the dominant species, with a concomitant decrease in species richness and diversity of co-occurring species. Main conclusion: Citizen science, alongside professional surveillance, has provided an effective method for studying invasion by H. axyridis, which is now well established and distributed across Chile. The rate of spread has been dramatic and the associated changes to the coccinellid community could disrupt the functioning, and ultimately resilience, of invaded ecosystems.