Extrusion of masses of yolk during embryonary development of the fruit flyAnastrepha fraterculus

Summary Eggs of the fruit fly Anastrepha fiaterculus (Diptera; Tephritidae) present an extensive variation in size. On average, they measured 1,415±86 μm in length and 241±16 μm in diameter. In vivo analysis of the embryonic development showed that, during gastrulation, the embryos may extrude a mass of yolk from their posterior end. Later on, during the development of the head, a similar mass may also be extruded from the anterior end. Four types of embryos were found: (1) embryos with masses at both ends; (2) embryos with only the anterior mass; (3) embryos showing just the posterior mass and (4) embryos without any mass. They occur in different frequencies in a sample of embryos collected from a population cage in which type 1 embryos were the most common. The masses varied in size, there being no significant differences between the anterior and posterior ones, nor among masses from different types of embryos. The masses are made of yolk material and contain a variable number of vitellophages. Hoechst staining revealed the presence of symbiont bacteroids in the masses. Electron microscopy confirmed these results. Just before hatching, the larva eats the anterior mass, then makes a 180° turn inside the egg, ingests the posterior mass and finally hatches near the posterior pole of the egg. The extrusion of the masses and the complex behavior of the larva may be related to the mechanism of bacterial infestation in this species.