Physiological status and change of cytoplasmic lipid droplets in the pheromone-producing cells of the silkmoth, Bombyx mori (Lepidoptera, Bombycidae)

Changes in size and number of cytoplasmic lipid droplets were quantified in the pheromone gland (PG) of Bombyx mori before and after adult eclosion. T wo days before eclosion, size and number of droplets are small (diameter is 2-7 mum) and few. The formation and significant proliferation of larger dr oplets (5-12 mum) take place between 2 days and I day before eclosion. From the day of emergence until day 3 a fluctuation in size and number of lipid droplets during the photophase (4 h intervals) is observed. The changes ar e more characteristic and dramatic on the day of emergence and first day, w hile attenuation of these changes can be observed from the second day and s eems to disappear by day 4. Bombykol content, at each respective time, is i n good correlation with the observed fluctuation in lipid droplet parameter s. Highest bombykol production daily is observed towards the early evening, when lipid droplets are the smallest (2-4 mum) and most numerous. By day 4 , however, this regularity also ceases. In 24 It old mated females PG cell structure is quite similar to newly emerged ones. In glands of 72 h old dec apitated females the formation of 'extra' large lipid droplets is remarkabl e. In vivo pheromone biosynthesis activating neuropeptide (PBAN) treatment, however, induced the formation of many small droplets, although numerous l arger ones also remained. The morphological changes in lipid droplets and c ellular dynamics associated with the external signal of PBAN in the PG sugg est a storage-pool function of the lipid droplets. (C) 2001 Elsevier Scienc e Ltd. All rights reserved.