Multifunctional perennial flower strips promote parasitoid wasps and other beneficial insects

Abstract: Subsidies for biodiversity promotion areas were implemented in Switzerland in 1994 to balance negative impacts of agriculture practice on biodiversity. This study examines and compares floral availability (volume) and beneficial insects (abundance) in two types of such areas: perennial wildflower strips and multifunctional perennial flower strips. The wellestablished wildflower strips were designed to foster biodiversity; the recently composed
multifunctional strips intend to specifically promote natural enemies and pollinators. Seven to eight strips of each type were selected on the Swiss Central Plateau, and data on flower volume and insect abundance and diversity were collected over two years. The three-year-old
multifunctional strips were compared to the equally aged wildflower strips. As predicted,
similar flower volumes were observed in both strip types. The comparison between
multifunctional and wildflower strips revealed a surprising similarity between the examined
insect groups with no significant difference in beneficial insects. Contrary to expectations, the
total flower volume in multifunctional strips did not drop from the second to the third year, and the volume of flowers with easily accessible nectar also remained stable. Despite this continuity in the flower volume, the abundance of pest controlling insects like parasitic wasps increased significantly and the numbers of pollinators dropped. The results highlight the importance of perennial strips for natural pest enemies but also the need for flower strips of various ages within the arable landscape matrix.