Lipid droplets in the pheromone glands of bombycids: Effects of larval diet on their size and pheromone titer

[Display omitted] •Lipid droplets (LDs) in pheromone glands (PGs) store fatty acid pheromone precursors.•Fatty acid content in the larval diet affected LD size and number in Bombyx mori.•The sex pheromone titer was affected by dietary fatty acid levels to a lesser degree.•LDs were found in the PG of Trilocha varians, the closest non-congener of B. mori.•LDs in PGs play an important role in the regulation of sex pheromone titer. In addition to the blend ratio, the quantity of sex pheromone components secreted by female moths may affect the efficient attraction of conspecific males. The present study using the silkmoth Bombyx mori, which has bombykol as its pheromone component, demonstrated that pheromone titer, body weight, and lipid droplet (LD) diameter in the pheromone gland were affected by the larval diet. Although the artificial diet contained approximately 11-fold more total fatty acids than mulberry leaf, the pheromone titer in the group fed the artificial diet (group AD) was approximately 2-fold higher than that of the group fed mulberry (group M). The diameter of LDs, which store the pheromone-precursor fatty acyl, E10,Z12-16:Acyl, was also larger in the AD group. The relatively small increase in sex pheromone titer by feeding on a fatty-acid-rich diet may be partly attributable to the storage of excess precursors in the LDs. We detected LDs in the pheromone glands of Trilocha varians, the closest non-congener of B. mori available in Bombycidae. T. varians uses bombykal and bombykyl acetate as sex pheromone components, which are biosynthesized via the same precursor fatty acyl as that of B. mori. The presence of LDs in T. varians suggests that the storage and mobilization mechanisms of the pheromone precursor fatty acyl via LDs may be conserved in bombycids.