Aphid biological control in arable crops via flower strips: The predominant role of food resources over diversity effects

Plant taxonomic and functional diversity promotes interactions at higher trophic levels, but the contribution of functional diversity effects to multitrophic interactions and ecosystem functioning remains unclear. In agroecosystems, flower strips can be sown to promote biodiversity and associated services, but their plant composition is poorly considered from a functional diversity perspective so as to promote multitrophic interactions. In a field experiment, aphid biological control was compared across contrasting flower strip mixtures, over a 4‐year arable crop rotation. The effects of plants providing food resources, that is nectar and legumes supporting alternative hosts and prey, and the effects of plant species richness and functional dispersion were investigated on the biological control of aphid populations. In general, increases in the percentage of plant cover providing nectar and alternative prey (Fabaceae) to natural enemies increased predator–prey ratios and aphid parasitism and decreased aphid population growth rates. These effects however depended on the crop species. Species richness and the functional dispersion of traits involved in plant–arthropod interactions were of lesser importance, and the directions of their effects were crop‐specific. Synthesis and applications . These findings provide useful insight for designing perennial plant mixtures for creating or restoring habitats supporting aphid regulation. It is not adequate to sow any mixture containing simply flowering plants. Plant mixtures should comprise a large proportion of plant species supporting alternative prey, like legumes, and species producing nectar being easily accessible to natural enemies (corollas with nondeep nectar). To be efficient over a crop rotation, with aphids being present at different seasons, these nectar resources should be provided throughout the year thanks to a diversity of plant flowering periods. La diversité taxonomique et fonctionnelle des plantes favorise les interactions aux niveaux trophiques supérieurs, mais la contribution des effets de la diversité fonctionnelle aux interactions multitrophiques et au fonctionnement des écosystèmes reste incertaine. Dans les agroécosystèmes, des bandes fleuries peuvent être implantées pour favoriser la biodiversité et les services associés, mais leur composition végétale est peu réfléchie sous un angle de diversité fonctionnelle de manière à favoriser les interactions multitrophiques Dans un essai en parcelle