Five Years of aphidophagous species sampling in belgian corn

The community of aphidophagous species present in agroecosystems is disturbed since the introduction of an exotic species the Multicoloured Asian Ladybird, Harmonia axyridis Pallas (Coleoptera: Coccinellidae). In this intensive agricultural area, five aphids predator species are commonly observed: three coccinellids H. axyridis, Coccinella septempunctata, Propylea quatuordecimpunctata, one hoverfly Episyrphus balteatus, and one lacewing Chrysoperla carnea. This study focuses on the occurrence of the five most abundant aphid predators and their seasonal abundance in corn. The abundance of adults and larvae of these species was evaluated over a five-year period, from 2009 to 2013. The sampling method consisted in the counting of aphids and all developmental stages of aphidophages present in quadrats of 1m² from April to November. Densities of aphid predators changed during five years studies. Since 2011, H. axyridis was the most abundant aphids predators in corn. H. axyridis numbers were found to increase over the first four inventoried year, reaching in 2012 86% for adult stage (119,7±7,8 adults/100m2) and 76% for larvae stages (242,8±14,2 larvae/100m2) of the aphid predators, while in 2009 these ratios were 14% and 23% respectively. For C. septempunctata and P. quatuordecimpunctata the population densities decrease at the end of the five years period. Population densities of C. carnea and E. balteatus were variable during the sampling period but increased in 2013. Phenology of the five studied species presents similar curves following the aphid abundance. The most abundant observed aphids were metopolophium dirhodum, rhopalosiphum padi, rhopalosiphum maidis, sitobion avenae and sitobion fragariae. H. axyridis starts reproducing after the peak in aphid population, suggesting that H. axyridis is able to complete its development by feeding on alternative prey such as larvae and pupae of conspecific and heterospecific. H. axyridis is a bivoltine species but the second generation was stop by the corn harvesting.