Field efficacy of aqueous and alcoholic neem seed extracts against Ommatissus lybicus de Bergevin (Hemiptera: Tropiduchidae) on ‘Mazafati’ date palm

Abstract

Neem ( Azadirachta indica A. Juss) is a highly valued botanical source of azadirachtin and other limonoids, which possess potent insecticidal, antifeedant, and growth-regulating properties against a wide range of arthropod pests while remaining safe for beneficial organisms. The Dubas bug ( Ommatissus lybicus de Bergevin) is the most destructive pest of date palm across the Middle East and North Africa, causing substantial yield losses and driving over-reliance on synthetic insecticides. This study evaluated aqueous and alcoholic (methanolic) neem seed extracts (control; aqueous: 2.5, 5.0, 7.5, and 10.0% w/v; alcoholic: 1.5, 3.5, 5.5, and 7.5% v/v) applied once or twice at 15-day intervals against O. lybicus on ‘Mazafati’ date palm in Bam, Iran. The experiment was arranged as a factorial randomized complete block design with three replications. Results showed that double applications consistently outperformed single applications, reducing adult emergence by 62.4%, egg deposition by 60.5%, and F 1 nymph emergence by 57.6%. Alcoholic extracts showed markedly superior efficacy: EC₅₀ values were 45–52% lower than those of aqueous extracts, with a relative potency of 1.8–2.1. Double application of alcoholic extract at ≥ 3.5% achieved complete suppression of oviposition and F 1 nymphs (100% efficacy). Effect size analysis revealed that application frequency accounted for 94–99% of explainable variance. Leaf greenness index (SPAD) was strongly correlated with pest population parameters ( r > -0.89), and the most effective treatments restored leaf SPAD values to healthy levels (> 50). These findings demonstrate that optimized neem-based treatments provide potentially commercially viable, high-efficacy control of O. lybicus , establishing empirical benchmarks for sustainable date palm integrated pest management. Based on these results, double application of alcoholic extract at ≥ 3.5% concentration is recommended for commercial control.