High parasitoid diversity in remnant natural vegetation, but limited spillover into the agricultural matrix in South African vineyard agroecosystems

Abstract

The maintenance of remnant natural vegetation in agricultural landscapes is an important component of conservation programmes that promote farmland sustainability. Demonstrating the biodiversity value of remnant vegetation can support conservation initiatives in production landscapes. We assessed the diversity and assemblage structure of hymenopteran parasitoids in fragments of native scrubland (fynbos) within vineyard landscapes in the Cape Floristic Region of South Africa. We also aimed to detect positive effects of adjacent fynbos on vineyard parasitoids, such as elevated diversity at vineyard edges adjoining fynbos or evidence of parasitoid spillover into vineyards. Fynbos remnants had significantly higher parasitoid abundance and richness than neighboring vineyards, and supported assemblages distinct from those within vineyards. Parasitoid diversity in vineyards was not influenced by distance to remnant vegetation. Additionally, evidence for spillover was limited, as there were abrupt changes in assemblage structure at fynbos/vineyard boundaries. Surrounding vineyards therefore seem to have an isolating effect on parasitoids in remnants. This emphasises the need to increase the permeability of the vineyard matrix. Yet, our results show that remnants are important for retaining parasitoid diversity and provide refugia for certain species within the disturbed agricultural environment. Approaches that combine natural remnant conservation with arthropod-friendly activities in vineyards would be an effective way to support diverse and functional parasitoid assemblages at the landscape scale. Conservation of this diversity will be crucial for maintaining long-term ecological resilience in agricultural landscapes.