Are ladybirds affected by farming practices at different spatial scales?

Given the current decline of biodiversity, modern agriculture is facing a new challenge: ensuring the food supply of a human population increasingly large whilst maintaining the ecological balance of agro-ecosystems to preserve their sustainability. Because of a strong reduction of inputs, organic farming is considered as a promising solution to promote auxiliaries communities at field and landscape scales and ensure crop protection thanks to biological control service. The present study aims to measure the impact of agricultural practices (organic vs. conventional) and of their spatial organization on aphids and their natural enemies. Twenty 1km² landscapes were selected in Ille et Vilaine (Western France), characterized by varying surface areas of organic vs. conventional farming. In each landscape, ladybirds, carabids, parasitoids and aphids communities were sampled from April to July 2012 in one organic winter wheat field and one conventional winter wheat field. Moreover, detailed agricultural practices of sampled and surrounding fields were collected. At field scale, the results demonstrate a beneficial effect of organic practices on auxiliaries. This result seems to be due to a more favorable microclimate in organic fields thanks to the structure of the vegetation and the lack of pesticides. At landscape scale, the farming practices don't seem to affect insects communities.