Sequential deposition of yolk components during oogenesis in an insect, Aedes aegypti (Diptera: Culicidae)

Vitellogenesis in Aedes aegypti of uniform body size was followed at 27 degreesC in narrow time intervals throughout their first reproductive cycle by measuring the length, diameter, and volume of follicles and oocytes, the latter as an expression of the yolk mass (vitellus). Independent of all experimental conditions, a two-step process of elongation was recognized for both follicle length and yolk length, so that growth curves were consistently composed of two linear regressions with different slopes against time. Follicle lengths started to increase immediately after the blood meal, while oocytes took up to 6 h to show a measurable increase in yolk length. The first linear phase continued until 30 h, when yolk length reached 268 +/- 22 mum. At this point, a transition occurred where the linearity shifted sharply for the next 6 h to 2-4-times higher slopes for both regressions. This second growth phase represented a 40% elongation of oocytes and follicles. Then, both curves leveled off at their final size, characteristic of mature ovaries: 462 +/- 10 mum for oocytes, 489 +/- 11 mum for follicles. These values remained constant until oviposition.