Herbivore and parasitoid insects respond differently to annual and perennial floral strips in an alfalfa ecosystem

Abstract

Non-crop flowering habitats have the potential to support natural enemies and improve biological control of insect crop pests. However, these habitats can also harbor pests. We evaluated the impact of annual and perennial flower mixtures on insect communities within a field crop landscape. The experiment consisted of alfalfa planted adjacent to strips of either an annual flower mix, a perennial flower mix, or control grass. Arthropods were vacuum collected from both the habitat strips and the adjacent alfalfa five times throughout the growing season, identified and sorted into functional groups of herbivores, predators, and parasitoids. Richness and evenness were also calculated for parasitoids, and parasitism of alfalfa weevil was measured in alfalfa. Perennial habitats bloomed earlier in the season, but annual habitats had a greater total number of open blooms. Herbivores were more abundant in annual flower and grass strips in the early season than in perennial flowers, whereas predators did not differ between habitats. Parasitoid abundance and family richness increased throughout the season in annual flower habitats and remained steady in the perennial flower and grass habitats. Parasitoid community composition in perennial flowers was distinct from those in grass and annual flowers. Both annual and perennial flower mixes supported distinct parasitoid communities with no evidence of pest spillover into adjacent alfalfa crops, although natural enemy abundances and biocontrol services in the alfalfa also were unchanged. Both flower mixes are viable candidates for adoption in semi-arid irrigated agricultural landscapes depending on the specific goals of land managers.