Spot the Problem
Since 1916, the Harlequin Ladybird (Harmonia axyridis) was introduced widely across North America as a biological agent against aphids. The ladybird was considered to have the perfect characteristics for this role: large size, diverse dietary range and voracious larvae which are easy to rear. However, despite the best intentions, the Harlequin Ladybird was soon “spotted” in the wild causing problems.
Although the species can benefit us by controlling aphid populations in apple orchards and other crops, there are also negative consequences. As the ladybird is a generalist, it does not restrict its prey to aphids and therefore large populations can affect native non-target insect species. Given its size and adaptability, the Harlequin Ladybird displaces native species of coccinellids, out-competing them for resources. The species can also become a public nuisance in the winter when large swarms seek winter dormancy sites such as garages, houses and sheds. These swarms become active in the presence of central heating, disrupting people’s homes.
It took the ladybird just two years to colonise Georgia and spread into neighbouring states of Florida and South Carolina. The European invasion was an equal concern, with the ladybird found in 13 European countries by 2007. So what makes it so invasive?
Invasive Characteristics
The Harlequin Ladybird has several characteristics/traits which have facilitated the invasion across North America and Europe.
- Eurytopic Nature
Predominantly associated with arboreal habitats, particularly orchards, the species has been found to survive and thrive in agricultural landscapes and dense woodlands. This gives the Harlequin Ladybird the opportunity to exploit resources in a wide variety of habitats.
- Climate
Unlike other aphidophagous coccinellids, this invasive ladybird has a wide natural latitudinal and longitudinal range in Asia. Furthermore, the Harlequin Ladybird has been seen to survive and breed in sub-tropical climates of Florida to the colder environment of Canada. These findings are a cause for concern as it is clear that temperature will not restrict this species future spread.
- Multivoltine
Whereas many native coccinellids require a dormancy period before becoming reproductively mature, the Harlequin Ladybird does not and can in fact have several broods a year.
- High dispersal ability
The Harlequin Ladybird is highly dispersive, engaging in long migratory flights to and from winter dormancy sites. Its rapid colonisation of North America and Europe to date is testament to its dispersal potential.
- No natural enemies
It is known that several species of parasitic wasp prey on Britain’s native ladybirds. A recently published study monitored Harlequin and native seven-spot ladybirds for natural enemies over four years. The findings demonstrated that 18% of seven-spots were parasitized by wasps compared to only 2 % of the Harlequins. This study clearly demonstrates a lack of predation and natural enemies for this species, another likely cause behind its impressive success.
References:
Adriaens, T., San Martin G & Maes, D (2008). ‘Invasion history, habitat preferences and phenology of invasive ladybird Harmonia axyridis in Belgium Biological Control 53: 69 – 88
Colunga-Garcia and Gage 1998. Colunga-Garcia, M. & Gage, S.H. (1998) Arrival, establishment, and habitat use of the multicolored Asian lady beetle (Coleoptera: Coccinellidae) in a Michigan landscape. Environmental Entomology, 27, 1574–1580.
Comont, R. F., Purse, B. V., Phillips, W., Kunin, W. E, Hanson, M., Lewis, O. T., Harrington, R., Shortall, C. R., Rondoni, G & Roy, H. E (2013). ‘Escape from parasitism by the invasive alien ladybird, Harmonia axyridis’ Insect Conservation and Diversity
http://planetearth.nerc.ac.uk/news/story.aspx?id=1563&cookieConsent=A
Majerus M., Strawson, V., Roy, H (2006). The potential impacts of the arrival of the harlequin ladybird, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), in Britain. Ecological Entomology 31: 207-215
Wang, L.Y. (1986) Mass rearing and utilization in biological control of the lady beetle Leis axyridis (Pallas). Acta Entomologica Sinica, 29, 104.
Photo Credit: Harlequin Ladybird Swarm (Giles San Martin)