Essential oils of Pinus halepensis and P. heldreichii: Chemical composition, antimicrobial and insect larvicidal activity

Pines (Pinus spp.) are a potentially viable source of bioactive molecules. The present paper investigates the chemical composition as well as biological activity of the needle essential oils (EOs) of the two Mediterranean pines (Pinus halepensis and P. heldreichii). The EOs were tested against respiratory pathogenic bacterial strains isolated from human swabs. Furthermore, a subchronic test on Drosophila melanogaster was conducted to assess insecticidal potential of the investigated EOs against dipteran insects. Regarding the composition of the studied EOs, significant differences in relation to the major components as well as the content of the different terpene classes was observed. Sesquiterpenes and diterpenes were most present classes in the oil of P. halepensis, where (E)-caryophyllene and thunbergol were dominant compounds (32.2% and 29.2%, resp.). Oil of P. heldreichii was rich in monoterpenes, among which limonene (34.4%) followed by a-pinene (23.8%) make up more than 50%. Tested EOs showed inhibitory action against respiratory pathogenic bacterial strains in the range of 0.19-12.00 mg/mL (MICs) and bactericidal effect (MBCs) at concentrations from 0.50 to 12.00 mg/mL. Among two presently and four previously tested pine EOs, P. halepensis demonstrated the highest potential, which might be contributed to relatively unusual composition. Namely, the results suggested that diterpene alcohol thunbergol might be an important antimicrobial agent either alone or in combination with other compounds, which should be the subject of the future studies. On the other hand, toxicity of P. heldreichii oil towards developing Drosophila melanogaster larvae was low, while oil of P. halepensis did not show any signs of toxicity at concentrations up to 3%. The data indicated that total content of pinenes in the EO of the Pinus species is positively correlated to the inhibition of development and larvicidal activity in a fruit fly model.