Evaluating the Effectiveness of Two Methods to Control Leptoglossus occidentalis Heidemann, 1910 in Black Pine Stands

Abstract

Leptoglossus occidentalis (Hemiptera: Coreidae), an invasive pest native to North America, causes significant damage to coniferous seed production worldwide. This study evaluated the effectiveness of contact spray and Arborjet trunk injection methods for controlling L. occidentalis in black pine (Pinus nigra) seed orchards in Bursa-Karacabey, Türkiye. Abamectin (18 g/L), as insecticide, was applied to plots of 50 trees each in 2025, and 300 cones were harvested in November 2025 for seed fill and empty cone analysis. Statistical analyses included Kruskal-Wallis and Wilcoxon tests with Bonferroni correction. Seed fill percentages were 9.7% (control), 33.9% (spray), and 52.8% (Arborjet trunk injection). The Arborjet method yielded approximately 5.6 times higher seed fill than the control with the lowest coefficient of variation (17.2%). Empty cone ratios differed significantly among groups (Fisher’s exact test, P < 0.001), with 0% in the Arborjet group versus 12% in the spray group. Treatment type explained 63.3% of total variance (η² = 0.633), with very large pairwise effect sizes (Cohen's d = 1.33 to 3.42). These results demonstrate that systemic trunk injection should be prioritized over contact spray in seed orchards and gene conservation areas.