Augmenting flower trait diversity in wildflower strips to optimise the conservation of arthropod functional groups for multiple agroecosystem services

Abstract

Sown wildflower strips are increasingly being established in Europe for enhancing arthropod conservation and the provision of ecosystem services, including biotic pollination and natural pest control. Here we use floral traits to identify different plant functional effect groups. Floral resources were provided in four experimental levels characterised by a cumulatively increasing flower trait diversity and vegetation stand complexity. The first level consisted of a bare control strip, whilst in each subsequent level three wildflower species with different functional traits were added (Level 0: control; Level 1: three Apiaceae species; Level 2: three Apiaceae and three Fabaceae species; Level 3: three Apiaceae, three Fabaceae species, and Centaurea jacea (Asteraceae), Fagopyrum esculentum (Polygonaceae), Sinapis alba (Brassicaceae)). Plots with sown wildflower strip mixtures were located adjacent to experimental plots of organically-managed tomato crop, which is attacked by multiple pests and partially relies on bees for fruit production, and hence dependent on the provision of pollination and pest control services. Results obtained here show that the inclusion of functionally diverse wildflower species was associated with an augmented availability of floral resources across time, and this increased the abundance of bees and anthocorids throughout the crop season. Several natural enemy groups, such as parasitoids, coccinelids and ground-dwelling predators, were not significantly enhanced by the inclusion of additional flower traits within the strips but the presence of flower resources was important to enhance their conservation in an arable cropping system

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

“…* P < 0.05; *** P < 0.001. because these predators have different nutritional requirements and might react differently to different fl ower traits at different times. However, our fi ndings are consistent with Balzan et al (2014Balzan et al ( , 2016, who report that FD had no effect on the abundance of fl ower visiting natural enemies. Furthermore, these authors report that mixtures with intermediary FD support a higher natural enemy richness.…”

“…Furthermore, these authors report that mixtures with intermediary FD support a higher natural enemy richness. Balzan et al (2014Balzan et al ( , 2016 increased FD by increasing the diversity of fl ower corolla types, which determines the ability of natural enemies to benefi t from fl ower nectar (Vattala et al, 2006;Van Rijn & Wäckers, 2016). Insect abundance and diversity recorded in this study, however is not associated with FD based on seven traits.…”

“…Insect abundance and diversity recorded in this study, however is not associated with FD based on seven traits. Balzan et al (2014Balzan et al ( , 2016 suggest that the presence of certain species of plants, particularly those attractive to natural enemies (i.e., Apiaceae spp. in their case), might mask the effect of FD on fl ower visitors.…”

“…Therefore, it is hypothesized that mixing fl ower species with different values for these traits, generating a high functional diversity (FD) at the mixture level, will attract and support a high diversity and abundance of insects. Previous studies showed that plant mixtures with high FD benefi t both natural enemies and pollinators (Fontaine et al, 2006;Campbell et al, 2012;Balzan et al, 2014). However, the high FD in these studies was based on an increased diversity in types of corolla, which determines the availability of food resources.…”

Spatial diversification of agroecosystems to enhance biological control and other regulating services: An agroecological perspective

“…together, whereas parasitoids did not visit long corolla flowers and bumble bees were absent from short corolla flowers. Nevertheless, several recent studies did not report an increased diversity of flower-visiting insects with such a mixture, recalling that a high functional diversity at the mixture level does not necessarily enhance insect diversity (Balzan et al, 2014(Balzan et al, , 2016aHatt et al, 2017c;Uyttenbroeck et al, 2017). At the landscape scale, however, the increased density of flowering features such as hedgerows showed a positive effect on pest control by parasitoids and pollination (Dainese et al, 2017).…”