Differentiating the effects of organic management, pesticide reduction, and landscape diversification for arthropod conservation in viticulture

Abstract

Biodiversity loss is a main challenge for agricultural sustainability. Major drivers include local management and landscape simplification. Therefore, conservation measures aim to increase organic agriculture, reduce pesticide use, and increase the proportion of semi-natural habitats (SNH). Yet, it is important to understand the effects of such measures. We investigate how arthropod biomass, taxa richness, and community composition in Malaise trap samples are affected by organic management, pesticide use, and SNH in the landscape. The 32 studied vineyards were chosen in a crossed design of management (organic vs. conventional) and pesticide use (regular vs. reduced) along a gradient of landscape composition. Pesticide reduction by 55% was obtained by including half of the vineyards with fungus-resistant grape (FRG) varieties. Malaise trap samples were weighed and arthropods identified using metabarcoding. Surprisingly, biomass was almost one-third higher in conventionally managed vineyards compared to organic ones. Taxa richness increased by more than one third when the proportion of SNH in a radius of 1,000 m in the surrounding landscape increased from zero to 50%. Diptera richness tended to be 4% higher in conventionally managed vineyards and the richness of Hymenoptera was 9% higher in FRG varieties. Community composition changed with the proportion of SNH and differed between organic and conventional management. Overall, organic viticulture was not effective to enhance the arthropod community, which was dominated by flying insects in our study. Agricultural policies should therefore rather preserve and promote SNH in the surrounding in order to promote arthropod biodiversity in viticultural landscapes.