Mosquito embryos and eggs: polarity and terminology of chorionic layers

The development of genetically modified vectors refractory to parasites is seen as a promising strategy in the future control of endemic diseases such as malaria. Nevertheless, knowledge of mosquito embryogenesis, a pre-requi site to the establishment of transgenic individuals, has been presently neg lected. We have here studied the eggs from two neotropical malaria vectors. Eggs from Anopheles (Nyssorhynchus) albitarsis and Anopheles (Nyssorhynchu s) aquasalis were analyzed by laser scanning microscopy and scanning electr on microscopy and compared to those of Drosophila melanogaster. We verified basic conflicting data such as mosquito egg polarity and ultrastructure of eggshell layers. A 180 degrees rotation movement of the mosquito embryo al ong its longitudinal axis, a phenomenon not conserved among all Diptera, wa s confirmed. This early event is not taken into account by several present groups, leading to a non-consensual assignment of eggshell dorsal and ventr al poles. Since embryo and egg polarities, defined during oogenesis, are th e same, we propose to consider the flattened egg side as the dorsal one. Th e structure of Anopheles eggshell was also examined. Embryos are covered by a smooth endochorion or inner chorion layer. Outside this coat lies the co mpound exochorion or outer chorion layer, assembled by a thin basal lamella r layer and external tubercles. The terminology related to eggshell layers is discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.