Chemical composition of Laurus essential oils from different Macaronesian Islands and their ovicidal and larvicidal activities against armyworm

Abstract

Essential oils (EO) from the fresh leaves of Laurus novocanariensis (LN) from Madeira and of L. azorica (LA) from four Azorean Islands (S. Miguel-SMI, S. Maria-SMA, Pico-PIC and S. Jorge-SJO) were analyzed by gas chromatography – mass spectrometry (GC-MS). A total of 51 components were identified, accounting for 99.5 to 99.9% of the total EO, respectively. All the Laurus' EO investigated were dominated by monoterpenes, and were significantly rich in oxygen-containing terpenes. However, the EO of LA and LN species showed a distinct chemical profile, being the first one more complex, particularly in SMA population followed by SMI population [1]. Interest in the plants' EO was renewed with emerging demonstration of their insecticidal properties. All the Laurus' EO tested showed a high ovicidal activity against Pseudaletia unipuncta eggs (> 95% of mortality). The same holds true for the pure components linalool, α-terpinyl acetate and trans-cinnamyl acetate; these are among the main components only in LA-SMA (the first two) and in LA-SJO (the last one). Also, all the Laurus' EO showed strong insecticidal effect on fourth instar larvae (> 66% of mortality), with the exception of the LA-SJO, that caused a mortality rate of 46%. LA-SMA was the most effective in killing the larvae and showed the highest toxicity at 96h after treatment (LC50 = 11.54 mg/mL) followed by LA-SMI (LC50 = 37.08 mg/mL). Among the pure components, α-terpinyl acetate was the most toxic (LC50 = 8.05 mg/mL) followed by linalool (LC50 = 25.27 mg/mL) and α-pinene (LC50 = 36.71 mg/mL), being the last one the major Laurus' EO components, except for LA-SMA. These data show that some of the Laurus' EO and/or their bioactive compounds could be used as agrochemical agent against P. unipuncta, a serious pest on the Azores's pastures. Further studies are required to determine the mode-of-action of these essential oil products, through semi-field trials.