Comparative study of the eggshell of the fruit flies Dacus oleae and Ceratitis capitata (Diptera: Trypetidae).
In laboratory studies on 2 tephritids using light and electron microscopy, the egg shell of Dacus oleae (a pest of olive) was found to have a compact endochorion, while that of Ceratitis capitata (a pest of various fruits) had an endochorionic layer full of holes. The egg shells of both species had an innermost chorionic layer that appeared to be crystalline in substructure. The anterior pole in each case contained the micropylar canal, but in addition bore an elaborate 'cup' in D. oleae. Both species exhibited peroxidase activity in most egg-shell layers and, as in Drosophila melanogaster, it was thought that the enzyme caused covalent cross-linking of the egg-shell proteins producing a resilin-type configuration with rubberlike properties. The above features were related to specific structural functions of the egg shell during fertilization, oviposition and respiration of the embryo. Biochemical analysis showed that the 2 species had very few egg-shell proteins with similar molecular weights.