Early Nymph Emergence Index (ENEI) for Jacobiasca lybica: An environmentally driven early-warning tool for vineyard risk assessment

We address the increasing threat of Jacobiasca lybica in southern Italian vineyards through a minimal, top-down, physiologically based population framework with environmentally dependent parameters. Although stage-structured modelling, the use of multiple environmental drivers and the general concept of exploiting earlier developmental processes for early warning are well-established approaches, the novelty of this study lies in their species-specific integration and operationalization for the early-season risk assessment of J. lybica. We introduce the Early Nymph Emergence Index (ENEI) as a cumulative indicator of modelled egg-to-nymph emergence pressure. Unlike nymph density, which describes the damaging stage already present on leaves, ENEI summarizes the biological process that precedes nymph build-up and is calibrated to anticipate future crossings of nymph-based risk thresholds. The framework is applied to the Feudo Arancio vineyard in Sicily. The 2002 field dataset is used for a preliminary site-informed evaluation, while the 2000–2025 environmental record is used to calibrate ENEI thresholds under moving-window and full-history protocols. Using the adopted ENEI-based formulation, the 2002 hindcast shows that ENEI can provide measurable anticipation of low-, medium- and high-risk crossings derived from the available community-level nymph observations. Endpoint-elasticity and finite-range analyses indicate that warning timing is only modestly affected by variation in the baseline mortality coefficients, with shifts not exceeding two days, but is substantially more sensitive to the effective oviposition rate, development rates and selected environmental-response parameters.