Perennial Flowering Strips for Conservation Biological Control of Insect Pests: From Picking and Mixing Flowers to Tailored Functional Diversity

Abstract

Wildflower strips sown at field margins can attract and support natural enemies required for conservation biological control of insect pests in agroecosystems. By focusing on perennial flowering strips, the present review discusses ways to compose flower mixtures that attract and support a high abundance and diversity of flower-visiting natural enemies. It firstly recalls why a high abundance and diversity of natural enemies is needed to enhance biological control. Thereafter, This review describes and discusses the approach consisting of picking and mixing flower species to compose mixtures. In past research, an array of flowers has been screened in various experimental conditions to select those attracting and supporting natural enemies. These results helped to develop mixtures that have been sown in fields. Although these mixtures often succeeded in increasing the abundance of some natural enemies (e.g., zoophagous hoverflies (Diptera: Syrphidae)), they often failed in enhancing a high diversity of predators and parasitoids simultaneously. A better understanding of flower-natural enemy interactions has been possible by screening the effects of functional flower traits on insect behavior. These results, here reviewed, notably revealed that distinct natural enemies may respond to different values of a given trait. It led to hypothesize that a high functional diversity of mixtures should attract and support a high diversity of natural enemies. The results from field-based research showed that increasing functional diversity per se may not be the key to enhance natural enemy diversity in wildflower strips. Hence, we propose here that a tailored functional diversity, consisting of picking and mixing the functional trait values known to attract and support a high variety of natural enemy species, could guide the composing of flower mixtures.