The Harlequin Ladybird Harmonia axyridis: a beneficial new arrival or an unwelcome invader?
By Remy L. Ware and Michael E.N. Majerus, Department of Genetics, University of Cambridge
The harlequin ladybird Harmonia axyridis (plate 1) is a beetle belonging to the family Coccinellidae and is native to central and eastern Asia. This predatory ladybird has had a long history of use in biological control. Harmonia axyridis has been repeatedly released in North America since 1916 to control pest insects including aphids and scale insects. Following its biological establishment in the 1980s, it has become the commonest ladybird over much of North America and is now considered by many to be a pest. Various European countries have also recently become home to the harlequin ladybird, including France, Belgium, Germany, Luxemburg and the Netherlands. On the 19th September 2004, Ian Wright, a member of staff in the Department of Genetics, University of Cambridge, spotted an unusual ladybird in a pub garden in Essex. This was the first sighting of the harlequin ladybird in Britain (see press release).
The harlequin’s arrival accrued extensive media coverage, even making the front page of the Times. Headlines included phrases such as ‘the killer ladybird’ and ‘the deadly invader’. But why the negative response if this species has a track record as a successful controller of aphids, a significant crop pest in Britain as in many other parts of the world? In fact, many of the favourable attributes of H. axyridis in terms of biological control are potentially very detrimental from an ecological perspective, in addition to leading to some unfavourable consequences for humans.
1. Impact on non-target prey
Harmonia axyridis is polyphagous, meaning that it has a wide dietary range. Whilst preferring aphid and coccid prey, it will also accept many non-target species including other beetles, psyllids, adelgids and the eggs of lepidopterans (butterflies and moths). This means it can feed on other foods at times when aphids are less abundant, and so has a competitive edge on many other, more specialised predators of aphids – a possible threat to biodiversity.
2. Impact on other ladybirds
The greediness of the harlequin ladybird, coupled with a particularly long breeding season, means that it may have the potential to out-compete our native ladybirds. This potential is being realised in North America, where native species such as Coleomegilla maculata have suffered a decline since the arrival of H. axyridis. The harlequin will also prey upon immature stages of other ladybirds, an example of intra-guild predation (where two species that share the same prey – in this case aphids – also feed on each other). The harlequin has been reported to prey upon larvae of three common British ladybird species, the 7-spot, Coccinella 7-punctata; the 14-spot, Propylea 14-punctata; and the 2-spot, Adalia bipunctata in the US. So not only will the harlequin pose a competitive threat to British ladybirds, it may also become one of their predators.