Sex pheromone component ratio in the cabbage looper moth altered by a mutation affecting the fatty acid chain-shortening reactions in the pheromone biosynthetic pathway

Comparisons in the sex pheromone biosynthetic pathway were made between a normal (wild type) and mutant strains of the cabbage looper moth, Trichoplusia ni, maintained in laboratory colonies. The sex pheromone of normal cabbage loopers consists of the major component, (Z-7-dodecenyl acetate) and five minor compounds (all acetate esters) that are biosynthesized from fatty acid precursors by a combination of Δ11 desaturation, chain shortening, reduction and acetylation. The mutant strain is characterized by higher amounts of Z-9-tetradecenyl acetate and lower amounts of Z-7-dodecenyl acetate. Amounts of fatty acid precursor found in pheromone glands were determined and indicated that some precursors were not chain shortened in the mutant strain. Amounts of all 12 carbon fatty acids were lower in the mutant strain compared to the normal strain. Incorporation studies using radiolabeled precursors indicated that the Δ11 desaturase, reductase and acetyl-CoA: fatty alcohol acetyltransferase were not affected by the mutation. However, it appeared that chain-shortening steps in the biosynthetic pathway were affected in the mutant strain. An in vitro chain-shortening assay was developed using several different deuterium-labeled fatty acyl-CoAs as substrates to determine how the chain shortening reactions were affected in the mutant strain. The amount of labeled product was determined by gas chromatography-mass spectrometry. The normal strain preferentially chain shortened Z-11-hexadecenoyl CoA by two rounds of β-oxidation to Z-7-dodecenoyl CoA. The mutant strain showed lower levels of chain shortening and only one round of β-oxidation occured.