Fine structure of the egg-shell in two humpbacked flies, Megaselia scalaris and Megaselia spiracularis (Diptera: Phoridae)

Abstract

The present study deals with the fine structure of the shell in the main body of deposited eggs of 2 humpbacked flies Megaselia scalaris and M. spiracularis (Diptera: Phoridae). Eggs deposited within a period of 3 h were embedded for transmission electron microscopy. In ultrathin sections, the overall architecture of the egg-shell was qualitatively similar to that of Drosophila melanogaster. There were, however, a series of quantitative differences. A prominent vitelline membrane bordered the plasma membrane. The chorion consisted of a thin inner layer, pillars, and a thin outer layer. There was a prominent external layer consisting of finely granular material. A 6–7 layered crystalline layer, and an amorphous electron-dense layer separated the vitelline membrane and the chorion. Hypochlorit treatment was used in order to determine the nature of this electron-dense layer. While all chorionic elements were removed, the layer in question was resistent to hypochlorit treatment, and therefore corresponds most probably to the wax layer found in Drosophila eggs.