Trunk-tissue extract pH as a candidate host-associated physiological indicator of red palm weevil (Rhynchophorus ferrugineus) infestation in date palm (Phoenix dactylifera)

Introduction The red palm weevil ( Rhynchophorus ferrugineus Olivier) is one of the most destructive pests of date palm ( Phoenix dactylifera L.). Its larvae develop within trunk tissues, making timely assessment of infestation challenging. Host-derived physiological indicators associated with infestation under field conditions remain insufficiently explored. Methods This pioneering, cross-sectional field-based study investigated trunk-tissue extract pH as a host-associated physiological indicator of R. ferrugineus infestation across 42 date palm cultivars in three contrasting production regions of Saudi Arabia. Extract pH was related to infestation intensity and trunk chemical composition. An exploratory unit-level receiver operating characteristic (ROC) analysis evaluated whether pH could discriminate between cultivar–region units with higher (>5%) and lower infestation. Results Infestation pressure varied substantially among regions, with the highest incidence in Mahd Al-Dhahab (13.46%), followed by Qassim (4.79%). Extract pH was higher in infested (symptomatic) than in un-infested palms across all regions and was strongly and positively associated with infestation intensity across cultivar–region units ((r = +0.84), (R^2 = 0.71), (p < 0.001); (n = 42)), with consistently positive correlations within each region ((r = +0.77) to (+0.88)). Extract pH correlated negatively with potassium, sugars, and fiber and positively with ash content. It discriminated between cultivar–region units with higher and lower infestation (ROC AUC = 0.86, 95% CI: 0.74–0.95). Discussion Threshold-specific estimates at pH ≥ 5.80 may be optimistic because the threshold was selected using the full dataset. This threshold is preliminary and should not be used for field diagnosis or management decisions without independent external validation. Because the study was cross-sectional and infested palms were sampled after symptom development, the findings establish an association with infestation intensity rather than early or pre-symptomatic detection; elevated pH may partly reflect advanced tissue damage. Nevertheless, this pioneering investigation provides a foundation for exploring host-derived physiological indicators in field-based red palm weevil surveillance and integrating physiological monitoring, cultivar resistance, nutritional status, and complementary detection technologies within an integrated pest management (IPM) framework. Longitudinal studies involving asymptomatic palms, temporal monitoring, and independent field validation are essential to determine the predictive value and practical applicability of trunk-tissue extract pH.