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.

Cell cycle regulator, small silencing RNA, and segmentation patterning gene expression in relation to embryonic diapause in the band-legged ground cricket

“…Although cell cycle arrest is generally accepted as a hallmark 81 of insect diapause (Koštál, 2006), cell division phases in diapause have only been 82 investigated in a few species (Tammariello et al, 1998;Koštál et al, 2009;Nakagaki et 83 al., 1991;Champlin and Truman, 1998;Shimizu et al, 2018). In D. nigrofasciatus, many 84 nuclei in diapause eggs are immunoreactive to phosphorylated and acetylated histone 85 H3, which involves mitotic chromosome condensation or mitogen-induced gene 86 expression (Tanigawa et al, 2009). This indicates possible mitotic activity even during 87 embryonic diapause in this species.…”

The circadian clock gene (Clock) regulates photoperiodic time measurement and its downstream process determining maternal induction of embryonic diapause in a cricket

“…This species shows a clear maternal effect, in which females exposed to long-day photoperiods lay non-diapause-type eggs that develop into nymphs without interruption. In contrast, females maintained under a short-day photoperiod lay eggs that are destined to enter diapause, where development is arrested at the blastoderm stage (Goto et al, 2008;Tanigawa et al, 2009). When females are transferred from a short-day to long-day environment, they gradually reduce and increase the numbers of diapause-and non-diapause-type eggs laid, respectively,…”

Early Embryonic Development of the German CockroachBlattella germanica

“…Uniform blastoderms are found in holometabolan, paleopteran, and hemipteran insect embryos (with exceptions for certain lepidopteran [6,7] and coleopteran [8][9][10] embryos. Direct-differentiating blastoderms are typical of polyneopteran insect embryos (with exceptions for certain 4 orthopterans [11][12][13] and plecopterans [14]. Because the preponderance of research into early insect embryogenesis is concentrated in holometabolous model species with uniform blastoderms, there is a relative lack of information about how early patterning proceeds in insects with direct-differentiating blastoderms.…”