LB 33-278 - Essential oils of selected Melaleuca species evaluated and identified combining HPTLC and GC-MS

The Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann), is a devastating pest with a vast range of host plants worldwide. In Florida, USA, it has been kept under control with an integrated pest management (IPM) program that includes a network of monitoring traps and routine releases of sterile males. The current detection protocols use traps baited with a male parapheromone, Trimedlure (Scentry Biologicals, Inc., Billings, MT, USA). However, this chemical is costly and limited to a single supplier, making the identification of new alternative attractants a priority. Previous studies conducted in Miami, FL, USA, revealed that sterile male medflies are highly attracted to tea tree oil (TTO), an essential oil from Melaleuca alternifolia mostly used in pharmaceuticals and cosmetics. Bioassays with thin layer chromatography (TLC) fractions of TTO indicated that only certain components of the oil were responsible for this behavior. Preliminary TLC screening unveiled subtle differences among oils that could affect reproducibility. In this study TTOs from a variety of sources, as well as other Melaleuca oils, were evaluated on a CAMAG high-performance thin layer chromatography (HPTLC) system (Muttenz, Switzerland) using silica gel F254 plates as the stationary phase, hexane-ethyl acetate as the mobile phase, and a vanillin-sulfuric acid solution as the derivatizing reagent. Oil constituents were identified by comparing their retention factors to those of reference standards. Gas chromatography-mass spectrometry (GC-MS) analysis was also conducted on the oils using an Agilent GC-MS system (Santa Clara, CA, USA) with a 30m x 0.25mm x 0.25µm DB-5 column and 70eV. GC-MS identification was obtained by comparison against Mass Finder v.3, Adams, FFNSC-3, Wiley 12/NIST 2020, and SHRS in-house libraries. Our results demonstrated that HPTLC is a fast and robust method for the separation and identification of Melaleuca oils and their components. The ability to analyze multiple samples under identical automated conditions provided trustworthy, reproducible results comparable with GC-MS. Most oil constituents, except those uncolored or merged, were identified by HPTLC in less time and with minimum amount of solvent compared to other analytical methods. TLC is also non-destructive, which allows samples to be recovered and used in further experiments. This study highlights HPTLC as a reliable, adaptable, and ecologically friendly technique for analysis of Melaleuca and other essential oils.