title: Early embryonic development and diapause stage in the band-legged ground cricket Dianemobius nigrofasciatus.
abstract: The band-legged ground cricket Dianemobius nigrofasciatus enters diapause at an early embryonic stage when adults are reared under short-day conditions or the eggs are exposed to a low temperature. We examined the morphological features of the embryo during early development and determined the exact stage of entry into diapause. In non-diapause eggs, no periplasmic space was observed in the surface region and a small number of nuclei surrounded by cytoplasm (energids) were found among the yolk granules and lipid droplets 12 h after egg laying (AEL) at 25 degrees C. The energids sparsely but evenly populated the surface region at 40 h AEL, but there were some gaps between these energids. A continuous thin layer of nuclei with cytoplasm had completely covered the egg surface at 56 h AEL, suggesting that the blastoderm is formed between 40 and 56 h AEL. At 72 h AEL, we found a germ band at the posterior pole. Electron microscopy revealed clear cell membranes at 40 h AEL. Staining with rhodamine-dextran dye demonstrated that the cell membrane is formed when the nuclei appear on the egg surface at 12-24 h AEL. These results indicate that cellularization occurs before blastoderm formation. In diapause eggs, neither the embryonic rudiment nor germ band was formed, but a continuous layer of cells covered the egg surface. It is concluded that D. nigrofasciatus enters diapause at the cellular blastoderm.
authors.affiliation: Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Osaka, 558-8585, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Tanigawa
authors.forename: Keiji
authors.initials: K
authors.lastname: Matsumoto
authors.forename: Kouji
authors.initials: K
authors.lastname: Yasuyama
authors.forename: Hideharu
authors.initials: H
authors.lastname: Numata
authors.forename: Sakiko
authors.initials: S
authors.lastname: Shiga
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000818:Animals; D004625:Embryo, Nonmammalian / Q000648:ultrastructure; D047108:Embryonic Development / Q000502:physiology*; D006135:Gryllidae / Q000033:anatomy & histology / Q000196:embryology*; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence