Multitrophic interactions in Harmonia axyridis

Overview

Results

The team

Related information

So what's the problem?

Harmonia axyridis, the harlequin ladybird, is a polyphagous predatory coccinellid, native to central and eastern Asia. It has been widely released as a biological control agent of aphids in the field and greenhouses in both North America and Europe. Since its accidental establishment in North America in the 1980s and in Europe in the late 1990s, it has spread and increased dramatically so that it is now the dominant ladybird species in much of the USA, Canada and several West-European countries. Significant negative effects from the establishment of H. axyridis have been reported. Owing to its predatory and competitive abilities, H. axyridis can have strong negative effects on biodiversity, impacting on many non-target species, including native ladybirds and other aphidophagous insects but also non-pest aphids and other herbivorous insects. It may also affect humans directly by invading buildings in huge numbers to seek overwintering sites. Moreover, in North America, H. axyridis has been reported to damage fruit crops in late summer and to taint wine when inadvertently harvested and crushed with grapes.

What is this project doing?

At CABI Europe-Switzerland, the main objective of our research programme on Harmonia axyridis is to assess the impact of the invasive ladybirds on native ladybirds and other non-target organisms. Other objectives include the monitoring of its spread in Switzerland and a critical assessment of current and potential control methods and management strategies against the invasive ladybird.

The ecological impact of H. axyridis on native ladybirds is studied using two approaches. Firstly, a long-term experiment based on 45 permanent field sites located in three habitats (broadleaved and coniferous woodland and meadows) was set up to observe changes in populations of native ladybirds during and after the invasion of the Asian species. Secondly, we have developed a risk assessment method to determine which native ladybird species are potentially most at risk through competition with the invasive species. This method, developed in collaboration with the University of Cambridge, UK, is based on field observations and literature surveys on niche and habitat overlap, and on laboratory studies on intraguild predation. Laboratory and field cage studies are presently being carried out in Delémont to assess competitive interactions between the invasive species and native ladybird species and to understand the chemical and mechanical defence mechanisms shown by some native species. Similarly, tests are made to assess potential predation by H. axyridis on native butterflies.

Results so far

Our monitoring programme, based on personal surveys, the development of a network of collaborators and a project website, showed that the beetle spread very rapidly in Switzerland. While only one beetle had been found in 2004 and none in 2005, in 2006 it already reached ten Cantons and, in 2008, all Swiss Cantons had at least one record.

Our surveys at permanent sites in north-western Switzerland showed that, in 2007, H. axyridis had already become the most abundant ladybird on broadleaved trees and, in 2008, it was more abundant than all native ladybirds counted together. It has also become an abundant ladybird in agricultural fields and is also present, in lower numbers, in grasslands and on conifers.

From 2006 to 2009, we observed a continuous decrease in native ladybird populations but the role of H. axyridis in this decrease needs to be confirmed by several years of observations. Results on competitive interaction experiments showed that H. axyridis larvae prey upon eggs and larvae of most native ladybirds. However, H. axyridis can also act as an intraguild prey in the presence of ladybird species showing chemical or mechanical defence mechanisms.

Our risk assessments for native ladybirds suggests that the species most at risk are aphidophagous ladybirds found mainly on broadleaved trees and shrubs, such as species in the genera Adalia, Calvia and Oenopia.

Project Manager

Marc Kenis

Address: Rue des Grillons 1, CH-2800 Delemont, Switzerland

Tel: +41 (0)32 4214884

Email: m.kenis@cabi.org

Project Team

Dirk Babendreier

Address: Rue des Grillons 1, CH-2800 Delemont, Switzerland

Tel: +41 (0)32 421 4885

Email: d.babendreier@cabi.org