The fine structure of the egg shells of the cabbage maggot, Delia radicum L (Diptera: Anthomyiidae), and its relation with developmental conditions and oviposition site

The fine structure and evolution of the egg shells of the cabbage maggot, Delia radicum, were studied in a French strain. The chorion did not undergo any modification at oviposition and consisted of three layers, except for the longitudinal strip, where the outer layer was lacking. The vitelline membrane of the oocyte was transformed by densification after oviposition. Differences in the longitudinal strip of the chorion were found between three strains of D. radicum. The strip was 650 mu m long in the French strain and a Canadian strain, but only 250 mu m long in a Moroccan strain. We also studied the effect of relative humidity on the hatching rate of eggs of the French strain and found that low relative humidity decreased the hatching rate. Finally, the function of the longitudinal strip was discussed in relation to climatic conditions.