Partial elucidation of Trichogramma putative sex pheromone at trace levels by solid-phase microextraction and gas chromatography-mass spectrometry studies

Virgin females of the minute parasitoid wasp Trichogramma turkestanica produce about 2 pg/h of two putative sex pheromonal compounds. These compounds could be successfully sampled during 20-50 h with SPME from 1.8 mL vials, containing 50-110 wasps and analysed by GC-MS. Accurate mass measurements at the 1 ng scale were possible with an internal standard of sulphur. One compound with MW 236 was identified as a C17H32 hydrocarbon while the other compound was the corresponding allylic alcohol with composition C17H32O. The alcohol could be silylated on-fibre and its mass spectrum suggested the presence of a conjugated 2,4-diene moiety. A miniaturised solvent extraction system for SPME needles, using 5 μL of acetone in a microtube was developed. After reaction of the extracted volatiles with the dienophile 4-methyl-1,2,4-triazoline-3,5-dione (MTAD), GC-MS of the MTAD adducts confirmed the presence of a diene. Interpretation of the combined mass spectral data, in combination with retention indexes of both compounds on non-polar and polar columns, suggested 2,6,8,12-tetramethyltrideca-2,4-diene and 2,6,8,12-tetramethyltrideca-2,4-dien-1-ol as most probable structures. These compounds have not been described previously. Biogenetically, they are most likely polyketides made up of a C4 starter unit that has been elongated with C2 and C3 units. Further biological and synthetic studies are necessary to prove their role as sex pheromone, confirm the proposed structures and determine the correct stereochemistry of the double bonds and the methyl groups.