Phytochemical Composition, Biological Activities, and Toxicity of the Leaf Essential Oils Obtained from Eucalyptus grandis × Eucalyptus urophylla Cultivated in Malaysia

Abstract

This study aimed to evaluate the phytochemical composition, antimicrobial properties, mosquito larvicidal effects, and brine shrimp toxicity of essential oils obtained using hydrodistillation from the fresh and dried leaves of Eucalyptus grandis × Eucalyptus urophylla at two age groups. Leaves from trees aged 17 to 31 months old yielded more essential oils than those aged 40 to 50 months. Gas chromatography-mass spectrometric analysis revealed that 1,8-cineol (13.1% to 26.7%) and α-terpinyl acetate (18.3% to 26.1%) were the dominant components across all essential oils. All tested essential oils inhibited Gram-positive bacteria, yeasts, and the dermatophyte Trichophyton rubrum, but failed to exhibit activity against most of the tested Gram-negative bacteria and Aspergillus fumigatus. The minimum inhibitory concentrations ranged from 0.16 to 2.50 mg/mL for bacteria and 0.04 to 1.25 mg/mL for fungi, highlighting the greater antifungal efficacy of the essential oils. All tested essential oil samples were also active against third instar larvae of Aedes aegypti and Aedes albopictus, with median lethal concentrations of 52.3 to 134 µg/mL after 24 h, lower than that of against Artemia franciscana nauplii (209 and 222 µg/mL). Therefore, Eucalyptus grandis × Eucalyptus urophylla essential oils are potential larvicidal agents for mosquito control with low toxicity to aquatic organisms.