Predisposing factors and spatio-temporal dynamics in two co-occurring cone pests in Pinus pinea (Leptoglossus occidentalis and Dioryctria mendacella)

Aim of study: To assess the impact of the exotic western conifer seed bug Leptoglossus occidentalis (WCSB), and the native pine cone moth, Dioryctria mendacella (PCM), two pests simultaneously feeding on cones and nuts of Pinus pinea; to identify the potential exogenous and endogenous factors controlling the impact of each pest, and to evaluate the occurrence of synergies and trade-offs between the pests. Area of study: Spanish Northern Plateau. Material and methods: Annual data on cone, nut and severity from each pest, collected in an extensive net of 52 plots (250 trees) installed in pure-even aged forests of Pinus pinea, covering nine years (2013-2021). Given the structure of the data and the proposed conceptual modelling, structural equation modelling (SEM) and path analysis were used. Main results: We observed an increasing pattern on the severity due to WCSB in the recent years, which may affect over 60% of pine nuts, while PCM tended to show a constant pattern, affecting on average 20% of the cones. Rate of severity of each pest was directly affected by the average size of a single cone, which was controlled by annual rainfall and stand age. Moreover, rising temperatures and age also exerted a direct and positive effect over the rate of severity of both pests, while the total amount of available cones in the year exerted a direct and negative effect. Complex temporal interactions between pest severities were identified. Research highlights: Severity of both pests is influenced by exogenous and endogenous factors, which may be aggravated under scenarios of climate change. These results support adaptive silviculture aimed at maintaining high cone availability to dilute pest impact.