Do flower mixtures with high functional diversity enhance aphid predators in wildflower strips?

Abstract

Among the semi-natural elements in agricultural landscapes, wildfl ower strips sown at fi eld margins or within fi elds are potential habitats for the natural enemies of insect pests. As insects are sensitive to a variety of fl ower traits, we hypothesized that mixtures with high functional diversity attract and support a higher abundance and species richness of aphid fl ower visiting predators than mixtures with low functional diversity. During a fi eld experiment, repeated over two years (2014 and 2015) in Gembloux (Belgium), aphid predators (i.e., lacewings, ladybeetles and hoverfl ies) were pan-trapped in fi ve sown fl ower mixtures (including a control mixture, with three replicates of each mixture) of low to high functional diversity based on seven traits (i.e., fl ower colour, ultra-violet refl ectance and pattern, start and duration of fl owering, height and fl ower class, primarily based on corolla morphology). In both years, the species of fl owering plants in the sown mixtures (i.e., sown and spontaneous fl owers) were listed, and the realized functional diversity in each plot calculated. Over the two years, a high functional diversity was not associated with high abundance and richness of aphid predators. Moreover, ladybeetles, which made up the majority of the predators trapped, were more abundant in mixtures with very low or intermediate functional diversity at sowing, especially in 2014. We hypothesize that certain fl owers, which were abundant in certain mixtures (and not in those exhibiting the highest functional diversity), attracted predators and were suffi ciently abundant to support them. Our results present novel information that could be used for developing fl ower mixtures that provide effective ecosystem services, such as pest control.