Plant Volatiles and Essential Oils Induce Sex-Specific Behavioral Responses and Concentration-Dependent Toxicity in the Invasive Pest Bagrada hilaris

Bagrada hilaris (Burmeister) (Hemiptera: Pentatomidae) is an invasive pest that causes significant damage to Brassica crops worldwide. This study evaluated behavioral and toxicological responses of adults B. hilaris to plant volatiles and essential oils (EOs). Y-tube olfactometer assays revealed sex-specific responses to plant-emitted volatiles: females were repelled by Coriandrum sativum and Petroselinum crispum, while males responded to Pelargonium hortorum. Essential oils exhibited non-linear concentration-dependent effects, with C. sativum EO inducing repellency at 40–80 µg/µL and P. hortorum at 160–320 µg/µL. In contrast, repellency index was not influenced by sex, but strongly driven by concentration, with C. sativum and P. hortorum most effective, and P. crispum showing weaker yet consistent responses. Toxicity assays demonstrated greater male susceptibility, with lower LC50 and LC90 values for C. sativum and P. hortorum. Gas chromatography-mass spectrometry (GC-MS) analysis of EOs matrix identified linalool, β-citronellol, trans-geraniol, and myristicin as the predominant constituents. Importantly, repellency occurred at lower concentrations than mortality thresholds, indicating distinct behavioral and physiological mechanisms. These findings support integrating C. sativum and P. hortorum essential oils into sustainable pest management strategies for B. hilaris.