Changes in the appearance of the membrane delimiting the genital atrium of Lutzomyia migonei are described for the first time. Dissections of laboratory-bred females at different physiological stages (i.e. on emergence, after a bloodmeal and after oviposition) revealed clear and constant differences between the membranes of the parous and nulliparous flies. The state of the membrane can be used as an alternative method for accurately age-grading female sandflies. Dissection methods and a simplified technique to prepare parts of sandflies for examination in a scanning electron microscope are also presented.