Habitat use by crop pests and natural enemies in a Mediterranean vineyard agroecosystem

Abstract

Conservation of natural habitats within agroecosystems often enhances the abundance and species diversity of arthropod natural enemies, but does not necessarily improve the biological control of crop pests. Differences in habitat use between some natural enemies (favoring natural areas) and pests (aggregating on the crop plants), were proposed to underlie low pest control in spite of high abundance of beneficials. To test this hypothesis, we characterized the habitat use of important vineyard pests (European grapevine moths and vine mealybugs) and of natural enemies (parasitoid wasps and spiders), and compared natural enemy communities across habitats. Arthropods were sampled in five vineyards (from vines and from herbaceous vegetation), and from adjacent natural habitats, using pheromone traps, visual searches and vacuuming. European grapevine moth and mealybug populations were highest inside the vineyards, furthest away from natural habitats. The proportion of natural enemies out of all arthropods was highest in the natural habitats. Parasitoid diversity was highest in natural habitats, intermediate on herbaceous vegetation within vineyards, and lowest on vines, and their abundance was higher on herbaceous vegetation than on vines. The parasitoids' distribution between natural and agricultural habitats varied among morpho-species, and their community composition differed among habitats and sampling dates. Spiders were less common than parasitoids (2.9% vs. 14.4% out of all suction-sampled arthropods, respectively), yet similarly distributed. As hypothesized, natural enemies associated with herbaceous vegetation more strongly than did grape pests, and their community composition differed between natural habitats and vineyards. To support the full diversity of beneficial arthropods, non-crop herbaceous vegetation both around and within vineyards should be conserved.