Irrigation decreases flower cover and beneficial arthropod abundances in Mediterranean vineyards

Over the last decades, the use of irrigation in vineyards has grown exponentially in response to climate change. In the Mediterranean region, irrigation is the most widely used method of preventing water stress and high sugar content in grapes. However, little is known about potential irrigation effects on biodiversity. This study aims to understand the effect of irrigation on inter-row vegetation, on the abundance of beneficial arthropods and on the predation of pest insects. In the Luberon region of South-Eastern France, nine irrigated and nine non-irrigated vineyards were analysed. Drip irrigation was applied only during the two driest months of the growing season. We found lower flower cover in irrigated vineyards but no difference in species richness and total vegetation cover. Similarly, abundances of several beneficial arthropods were directly affected by irrigation, such as crab spiders, ladybirds, ladybird larvae and parasitic wasps. Structural equation modelling (SEM) revealed that negative irrigation effects on these arthropods were mediated by negative effects on flower cover. Predation rates were also lower in irrigated vineyards but only during daytime. Grapevine yield was not affected by irrigation. Experiments manipulating water availability under controlled conditions may help to understand this surprisingly strong effect of irrigation on flower cover and beneficial arthropod abundance.