Comparative study of the eggshell of the fruit flies Dacus oleae and Ceratitis capitata (Diptera: Trypetidae)

Abstract

The eggshell of two fruit flies of economic importance has been studied by means of light and electron microscopy. The eggshell of the olive fruit fly, Dacus oleae, contains compact endochorion, whereas that of the Mediterranean fruit fly, Ceratitis capitata, exhibits a holey endochorionic layer. The eggshells of both species have an innermost chorionic layer which appears to be crystalline in substructure. The anterior pole in each case contains the micropylar canal but in addition it bears an elaborate "cup" in Dacus oleae. Both species exhibit peroxidase activity in most eggshell layers and, as in the case of Drosophila melanogaster, it is thought that the enzyme causes covalent cross-linking of the eggshell proteins producing a resilin-type configuration with rubberlike properties. The above features are related to specific structural functions of the eggshell during fertilization, oviposition, and respiration of the embryo. Biochemical analysis has revealed that the two species have very few eggshell proteins that are similar in molecular weight.