Seven desaturase cDNAs were isolated from pheromone glands of Helicoverpa assulta, a moth producing a sex pheromone blend with high Z9-16:Ald and low Z11-16:Ald, opposite to what is found in other heliothine moths such as Helicoverpa zea. Six of the seven sequences map onto recently defined lepidopteran desaturase sequence lineages and the other is orthologous to a desaturase sequence previously reported only in H. zea. The levels of desaturase-encoding transcripts in pheromone glands were determined and the three most abundant ones were functionally expressed in a desaturase-deficient mutant strain of Saccharomyces cerevisiae. The HassNPVE transcript, shown to encode a delta9 desaturase producing more Z9-18:Acid than Z9-16:Acid, was the most abundant, followed by the HassKPSE transcript, shown to encode a delta9 desaturase producing more Z9-16:Acid than Z9-18:Acid, and by the HassLPAQ transcript, shown to encode a delta11 desaturase producing only Z11-16:Acid. Thus, the relative amounts of transcripts encoding two delta9 desaturases and a single delta11 desaturase in H. assulta pheromone glands were consistent with the relative amounts of unsaturated fatty acid precursors required to produce the major and minor sex pheromone components of this species. Desaturase transcript levels in pheromone glands were also found to be as high during scotophase as during light phase, when pheromone production ceases. The other four transcripts were present at extremely low levels in H. assulta pheromone glands and the functional roles of their encoded desaturase-homologous proteins could not be determined.