Wildflowers sown at field margins have positive and negative effects on pests and parasitoids

Wildflower strips are sown at field margins throughout Europe to support insect conservation in agricultural areas. Among other insects, parasitoids may favor a biological regulation of pests. On an experimental field of the research platform AgricultureIsLife in Gembloux (University of Liège, Belgium), three replications of five wildflower seed mixtures were sown in strips adjacent to crops in spring 2013. Insect pests and their parasitoids were pan-trapped in spring 2014 in both wildflower strips and oilseed rape crops and identified at the species level. Flower species and cover were monitored in the strips using 1 m² quadrats, before mowing. Meligethes spp. were found abundantly in crops when oilseed rape was blooming. Meligethes’ parasitoids occurred later and their abundance was positively correlated with that of Meligethes in the flower strips. At the crop ripening stage, weevils Ceutorhynchus spp. occurred and were followed by an increase in abundance of their parasitoids in both crops and flowers. Positive as well as negative correlations were found between the abundance of these pests, their parasitoids and different flower species blooming at this time. The link between these results with flower species’ functional traits will be discussed