The Invasion of the multicoloured Asian ladybird
9/10/12

Once used in the integrated aphid control, the multicoloured Asian ladybird – Harmonia axyridis – is today one of the most abundant species in our regions, even entering the very heart of our homes. But the scientific clever riposte is little by little being put together. Gembloux Agro-Bio Tech has just taken a decisive step in the identification of…the hydrocarbons which play a role in the formation of the animal’s Winter aggregations.

Who could have predicted such a scenario? The scientists maybe, had they been consulted. European horticulturists without a doubt, if they had taken a little more interest in the problems experienced in the United States several years previously. When the Belgian, French, Dutch, etc. horticulturists introduced the multicoloured Asian ladybird into their crops over the 1990s it was thought to be blessed with every virtue. Renowned for its voracity, Harmonia axyridis makes short work of theswarms of aphids that invade the greenhouses. Easy to breed, it does not cost much and has an undeniable advantage over insecticides: no toxicity for handler! Like the professionals before them, ordinary citizens also bought it, delighted to use this perfect auxiliary of the ‘integrated pest control’ against plant parasites  in their vegetable plots and gardens. Thus, preceded by its reputation as one of God’s good creatures (in French, the ladybird is called ‘bête à bon Dieu’ as well as ‘coccinelle’), the multicoloured Asian ladybird – it can indeed be yellow, red, orange or black – became, unknowingly, the symbolic standard bearer of all these ‘useful’ insects, loyal helpers for human beings, which it was necessary to protect at all costs.

Harmonia_axyridis

Invasive species

From 2001, people started to become disenchanted. Whilst the insect was thought unable to survive the rough Winters, it started to be noticed here and there in Flanders, out in the wild nature. Then in Brussels. Next in Wallonia. In hardly ten years, the ladybird spread extraordinarily quickly and ended up invading the whole country, a process which has today earned it its status as an invasive species.

A problem? Yes, and in three ways. First of all, the animal is an ‘intraguild’ predator. This means that, far from settling for devouring aphids (Hemiptera: Aphidoidea) and other small soft bodied insects, the multicoloured Asian ladybird does not hesitate to take on aphidophagous predators. It enters into direct competition with other insect species, including indigenous ladybirds, of which it devours the larvae. In this respect, the most recent scientific reports published in Belgium seem to indicate a decline in the two spotted and the ten spotted ladybirds, species which our  ecosystems have good need of.

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