The occurrence of multicolored ladybird, Harmonia axyridis Pallas, a biological control agent in agroecosystems in Wallonia

The Asian ladybird, Harmonia axyridis Pallas (Coleoptera: Coccinellidae), was imported in 1997 in Belgium to control aphid populations in greenhouses. It took only few years to the insect to get adapted to temperate climate conditions and to spread out all over Europe. Now, H. axyridis is one of the coccinellid with the biggest size in Belgium, causing damages to the ecosystems through e.g. intraguild predation (IGP).
We are still lacking information about the consequences of the introduction of this superpredator in our agro-ecosystems. This work focuses on the potential impacts of H. axyridis on the entomofauna associated with several crops (potatos, corn, wheat, broad bean). We evaluated in 2009 the occurrence as well as the interactions between aphids and their natural enemies (hoverflies, coccinellids and lacewings) in several agro-ecosystem sites in northern Wallonia.
After one year of field observations, were found thirteen coccinellid species, most of the catched individuals being H. axyridis with 64% of the coccinellids, Propylea 14-punctata, 15%, or Coccinella 7-punctata, 14%. This invasive ladybird dominates the group of coccinellids generally in all crops in north Wallonia.
The results with the sticky traps show that the maximum occurrence of H. axyridis in crops is observed in chicory, sugar beet and potatoes.
The relationship aphid-ladybird in wheat for example, brings out that increase of density of Asian ladybird in mid-July follow the increase of aphids (Sitobion avenae, Sitobion fragariae, Metopolophium dirhodum, Aphis fabae) in the end of June.
We also observe that, in most agro-ecosystems, hoverflies and lacewings are the dominant aphid natural enemies. In all crops investigate, the multicolored ladybird occurs with 5% of the aphidophagous after the Chrysopidae, 12% and the Syrphidae, 76%. In 2009, the agro-ecosystems with the most aphidophagous species are carrot and broad bean and these habitats are dominated by hoverflies.