Comparative study of the essential oils of four Pinus species: Chemical composition, antimicrobial and insect larvicidal activity

Comparative analysis of the chemical composition and biological activity of the essential oils from the needles of four Pinus species (P. mugo subsp. mugo, P. nigra subsp. nigra, P. sylvestris and P. peuce) from the central Balkans was performed. Although different chemical profiles of the dominant terpenes for each species were determined, essential oils were, generally, dominated by monoterpenes with a-pinene as one of the first two major volatiles. Tested oils showed inhibitory action against respiratory pathogenic bacterial strains, isolated from human swabs, in the range of 1.25-20.00 mg/mL (MICs) and bactericidal effect (MBCs) at concentrations from 2.50 to 40.00 mg/mL. Considering cell wall composition, there were no significant differences in sensitivity between Gram-positive and Gram-negative strains. In addition, the place of isolation did not provide evidences for higher susceptibility/resistance of the strains obtained from the particular infection site. On the other hand, toxicity of essential oils towards developing Drosophila melanogaster larvae was low, except P. mugo subsp. mugo oil, which did not show any signs of toxicity at concentrations up to 3%. Highest mortality of larvae and adults of D. melanogaster was noted for P. sylvestris essential oil with an estimated LC50 at the end of experiment (14 days) of 2.78% with a 95% confidence interval of 2.15-3.42%. Short-term 96 h LC50 values due to low mortality at larval stage could not be calculated for any oil and are expected to be much higher than 3%. According to the obtained antimicrobial activity and toxicity towards D. melanogaster, the oils can be arranged in the following order: P. sylvestris > P. peuce > P. nigra subsp. nigra > P. mugo subsp. mugo.