Ultrastructural studies on the pheromone-producing cells in the silkmoth, Bombyx mori: formation of cytoplasmic lipid droplets before adult eclosion

The regulation of Δ11-desaturase gene expression in the pheromone gland of Mamestra brassicae (Lepidoptera; Noctuidae) during pheromonogenesis

Cabbage moth (Mamestra brassicae) females produce sex pheromones to attract conspecific males. In our M. brassicae colony, the pheromone blend is composed of Z11-hexadecenyl acetate (Z11-16Ac) and hexadecyl acetate (16Ac) in a 93:7 ratio. A fatty acyl Δ11-desaturase is involved in the production of the main pheromone component. The release of Pheromone Biosynthesis Activating Neuropeptide (PBAN) regulates the pheromone production in the pheromone gland (PG). We cloned a cDNA encoding the MambrΔ11-desaturase and analyzed its expression profile over time in M. brassicae tissues. Transcript levels of the Δ11-desaturase in larvae, pupal PGs, fat body, brain and muscle tissues were <0.1% of that in female PGs, whereas expression in male genitalia was 2%. In the PGs of virgin females the expression level increased continuously from eclosion to the end of the 1st day when it reached a plateau without further significant fluctuation up to the 8th day. In contrast, we recorded a characteristic daily rhythmicity in pheromone production with a maximum around 200 ng Z11-16Ac/PG. In some experiments, females were decapitated to prevent PBAN release and thereby inhibit pheromone production, which remarkably increased after treatment with Mambr-Pheromonotropin. Further experiments revealed that mating resulted in a significant suppression of pheromone production. However, expression of the Δ11-desaturase was not affected by any of these interventions, suggesting that it's not regulated by PBAN. Fluorescent microscopy was used to study the potential role of lipid droplets during pheromone production, however, no lipid droplets were identified indicating that pheromonogenesis is regulated via de novo fatty acid synthesis.

Studies of sex pheromone production under neuroendocrine control by analytical and morphological means in the oriental armyworm, Pseudaletia separata, Walker (Lepidoptera: Noctuidae)

Most female moths produce species-specific sex pheromone blends in the modified epidermal pheromone gland (PG) cells generally located between the 8 and 9th abdominal segments. The biosynthesis is often regulated by pheromone biosynthesis activating neuropeptide (PBAN) either in or prior to de novo fatty acid synthesis or at the formation of oxygenated functional group. In Pseudaletia separata, information about life span, calling, PG morphology, daily fluctuation of pheromone production and its hormonal regulation is limited. We measured pheromone titer daily (16:8; L:D) at 2h intervals in scotophase. Blend ratio stabilized during the 2nd day (till 4-5th) at 6th hour of scotophase, with the ratio of 27.5:12.8:44.4:15.3 for Z-11-16OH:16OH:Z-11-16Ac:16Ac, respectively. Females showed calling behavior from this time. We found with light and fluorescence microscopy that PG consisted of intersegmental membrane (A part), and dorso-lateral region of 9th abdominal segment (B part), encountering for ∼ 35% of total production revealed by gas chromatography. Ratios did not reveal difference. We did not find precursor (triacylglycerols) accumulation in form of lipid droplets, implying that PBAN stimulates de novo biosynthesis of 16:acyl precursors. In vivoHez-PBAN injections (1-3 × 5 pmol, 2h intervals) into 3 days old 16-18 h decapitated females stimulated pheromone production, both in A and B parts. Blend analyses including ratios suggest stimulation of the initial phase of synthesis, but desaturation of fatty acyl intermediates do not follow proportionally. More saturated fatty acid is converted from the available pool to the final OH and Ac, compared to females kept intact in scotophase. In vitro studies (PGs incubated 4-6h in the presence of 0.25 or 0.5 μM Hez-PBAN, especially with surplus 2mM malonyl-CoA) revealed higher saturated component ratio than the unsaturated, compared to natural blend or in vivo injections.