Update on the Alien Harlequin Ladybird
The spread of the harlequin ladybird Harmonia axyridis from its native range (Russia, Mongolia, China, Japan) is considered one of the fastest global insect invasions. The harlequin was deliberately released in various European countries to control pest insects and was first recorded in Britain in 2003. It arrived here from Europe and North America with produce and by means of flight and wind. The harlequin is a large, voracious, feeding and habitat generalist. It out-competes most of the other 46 ladybird species resident in Britain for food (aphids) and predates the eggs and larvae of ladybirds and other insects.
The harlequin spread very fast (moving northwards at about 100 km per year) in the first few years of colonisation. It is now firmly established over much of Wales and all of England as far north as North Yorkshire. There are also many scattered records of the species across northern England and Scotland. Although there is some effect of lower recording in these more sparsely populated regions, the establishment of this species seems to be limited north of the Pennines. The same is true of many native ladybird species, which like warm and moderately dry conditions. So, whilst there are records of the harlequin as far north as Orkney and Shetland, there is no evidence that the species successfully breeds north of Glasgow. The main invasion front of the harlequin reached its northern limit a few years ago.
Regarding the dominance of the species in areas further south, the story is mixed. The harlequin is certainly thriving in many areas, but the situation is patchy and some recorders have seen numbers drop in recent years. For example, in regular standardised surveys in East Anglia, harlequins reached a peak in 2009, accounting for over 40% of all ladybirds, but dropped back to 24% in 2011. This was partly due to the 7-spot ladybird, our most common species, bouncing back after some poor years. The 7-spot is a large ladybird that has a rather different niche to the harlequin, and has probably not been affected in a major way by the arrival of the alien species. Unfortunately the same is not true of all other ladybirds, some of which suffer predation by the harlequin. The small 2-spot ladybird seems to have been most severely affected and has shown to be in decline here and elsewhere in Europe. In Britain we have carried out molecular work confirming that harlequin larvae feed on 2-spot (and 10-spot) ladybird larvae and believe that this explains part of the reason for the observed 2-spot decline.
There is still no clear solution to tackle the harlequin problem, with possible control ideas lacking efficacy-testing and are either too expensive (pheromone traps) or too risky (introduction of a mite that makes female harlequins sterile). Natural control by native predators (e.g. spiders), parasitoids (e.g. the braconid wasp Dinocampus coccinellae) or diseases (e.g. fungal pathogens), is the best hope. The evidence is that these attack harlequin ladybirds to a lesser extent than they do native ladybirds. Additionally there is little evidence to suggest that natural enemies play a major role in regulating ladybird populations. Nevertheless, over time natural enemies may adapt and control harlequin numbers more effectively. In the meantime, we will have to live with our attractive but unwelcome arrival.
Please submit records of any ladybird species to www.ladybird-survey.org (ideally with a photograph for verification).
Peter M.J. Brown & Helen E. Roy, UK Ladybird Survey