Climatic factors, landscape composition and host plant traits co‐drive fruit infestation of unmanaged walnut trees by the invasive pest fly Rhagoletis completa ( C resson, 1929) ( D iptera: T ephritidae)

Abstract Rhagoletis completa (Cresson, 1929) is a North American invasive pest fly infesting walnut fruits ( Juglans spp.). The abiotic and biotic factors driving its population dynamics and associated fruit damages remain poorly understood. This study aimed, for the first time, to disentangle the relative effects of meteorological conditions, landscape characteristics, local environment and host plant traits on the abundance of this non‐native pest in a European country. A total of 2433 walnut fruits were sampled and multiscale environmental variables were measured between July and December 2023 across 24 sites in northern France. Generalised linear mixed models were used to explore the relationships between the presence and abundance of the pest and the multiple environmental variables measured across various temporal and spatial scales. Fruit infestation was positively associated with local factors, including large‐sized fruit, walnut tree abundance and landscape characteristics such as the proximity of grasslands and the density of corridors (hedgerows, rivers). In contrast, it was negatively impacted by anthropogenic habitats such as conventional crops and orchards. Infestation rate was also affected by climatic variations, positively by the mean minimum temperature over the preceding 14 days and negatively by the heavy rainfall in the spring season. Our study revealed high infestation rates of unmanaged walnut trees in northern France and showed that these trees growing spontaneously outside production areas can serve as wild reservoirs for Rhagoletis completa . Therefore, such unmanaged trees should be considered in Integrative Pest Management strategies to limit crop infestations.