Identification of insecticidal constituents of the essential oils of <i>Dahlia pinnata</i> Cav. against <i>Sitophilus zeamais</i> and <i>Sitophilus oryzae</i>

<div><p>The aim of this research was to determine the chemical composition of the essential oils of <i>Dahlia pinnata</i>, their insecticidal activity against <i>Sitophilus zeamais</i> and <i>Sitophilus</i><i>oryzae</i> and to isolate insecticidal constituents. Based on bioactivity-guided fractionation, active constituents were isolated and identified as d-limonene, 4-terpineol and α-terpineol. Essential oils and active compounds tested exhibited contact toxicity, with LD₅₀ values ranging from 132.48 to 828.79 μg/cm² against <i>S</i>. <i>zeamais</i> and <i>S</i>. <i>oryzae</i>. Essential oils possessed fumigant toxicity against <i>S</i>. <i>zeamais</i> and <i>S</i>. <i>oryzae</i> with LC₅₀ from 14.10 to 73.46 mg/L. d-Limonene (LC₅₀ = 4.55 and 7.92 mg/L) showed stronger fumigant toxicity against target insects. 4-Terpineol (88 ± 8%) and d-limonene (87 ± 5%) showed the strongest repellency against <i>S</i>. <i>zeamais</i> and <i>S</i>. <i>oryzae</i>, respectively. The results indicate that essential oils and insecticidal constituents have potential for development into natural fumigants, insecticides or repellents for control of the stored-product insect pests.</p>