Location of micropyles and early embryonic development of the two‐spotted cricket Gryllus bimaculatus (Insecta, Orthoptera)

Abstract

Early embryogenesis of the two-spotted cricket Gryllus bimaculatus was examined by scanning electron microscopy and several fluorescence staining methods, with special reference to these four issues: (i) the location of micropyles; (ii) the transfer of the female pronucleus following meiosis; (iii) the timing of cellularization; and (iv) the process of the germ primordium formation. Between two and four micropyles lie in the mid-ventral region of the egg. The egg nucleus is at the mid-dorsal periphery of the new laid egg, and meiosis resumes and is completed there. The female pronucleus moves to the mid-ventral side, and fertilization occurs there. Energid starts to proliferate and migrates to the periphery of the egg, initiating blastoderm formation. Actin caps surround each superficial nucleus. Cellularization occurs during the blastoderm stage. At a late blastoderm stage, nuclei aggregate in both the posterolateral patch-like regions of the egg to form a germ primordium. The germ primordium looks like a pair of dumbbells. Both the patches shift towards the ventral side and fuse into a germ primordium. The germ primordium contracts to produce a clearly delineated germ band. Observations on distribution patterns of F-actin indicate that, all through the process, the germ primordium retains that unity, and is not separated into two parts.

Early embryonic development and diapause stage in the band-legged ground cricket Dianemobius nigrofasciatus

“…It has been reported in many species that the cellular blastoderm appears after the syncytial blastoderm (Anderson 1972b;Schweisguth et al 1991;Schejter and Wieschaus 1993;Handley et al 1998;Sarashina et al 2005). Current studies suggest the occurrence of cellularization before completion of blastoderm is unique to D. nigrofasciatus and S. gregaria among hemimetabolous and holometabolous insects (Ho et al 1997).…”

“…Both types of blastoderm formations have been reported in Orthoptera. The cricket species A. domestica and G. bimaculatus exemplify the uniform blastoderm formation; the locust species S. gregaria, the differentiating blastoderm formation (Sauer 1966;Ho et al 1997;Sarashina et al 2005). In D. nigrofasciatus, the first few mitoses occurred within the Fig.…”

“…Cellularization occurs shortly after the nuclei move to the egg surface and before they completely enclose the whole egg, indicating that it occurs before blastoderm formation (Ho et al 1997). In G. bimaculatus, cellularization occurs during the blastoderm stage, indicating that the cellular blastoderm follows a syncytial blastoderm (Sarashina et al 2005). In non-diapause eggs of D. nigrofasciatus, the blastoderm is formed between 40 and 56 h AEL.…”

“…Shortly after the nuclei move to the surface but before blastoderm formation, they become surrounded by the cell membrane. In the cricket Gryllus bimaculatus (Orthoptera: Gryllidae), however, it has been shown that cellularization occurs during the blastoderm stage by using a fluorescent lipophilic tracer for labeling the cell membrane (Sarashina et al 2005). It has also been reported that the cellular blastoderm appears after the syncytial blastoderm in Acheta domestica (Orthoptera: Gryllidae) (Handley et al 1998).…”

Evolution of insect development: to the hemimetabolous paradigm

“…Its early developmental processes are illustrated in Figure 2. At 27 hAEL, after formation of a cellular blastoderm, the number of nuclei per unit area increases in the posterolateral region (bipartite germ anlage), and a large patch of closely adjacent nuclei was observed on each egg flank [22]. At 28 hAEL, the bipartite germ anlage starts to merge from the posterior side.…”