Embryonic development of Eucorydia yasumatsui Asahina, with special reference to external morphology (Insecta: Blattodea, Corydiidae)

Abstract

As the first step in the comparative embryological study of Blattodea, with the aim of reconstructing the groundplan and phylogeny of Dictyoptera and Polyneoptera, the embryonic development of a corydiid was examined and described in detail using Eucorydia yasumatsui. Ten to fifteen micropyles are localized on the ventral side of the egg, and aggregated symbiont bacterial "mycetomes" are found in the egg. The embryo is formed by the fusion of paired blastodermal regions, with higher cellular density on the ventral side of the egg. This type of embryo formation, regarded as one of the embryological autapomorphies of Polyneoptera, was first demonstrated for "Blattaria" in the present study. The embryo undergoes embryogenesis of the short germ band type, and elongates to its full length on the ventral side of the egg. The embryo undergoes katatrepsis and dorsal closure, and then finally, it acquires its definitive form, keeping its original position on the ventral side of the egg, with its anteroposterior axis never reversed throughout development. The information obtained was compared with that of previous studies on other insects. "Micropyles grouped on the ventral side of the egg" is thought to be a part of the groundplan of Dictyoptera, and "possession of bacteria in the form of mycetomes" to be an apomorphic groundplan of Blattodea. Corydiid embryos were revealed to perform blastokinesis of the "non-reversion type (N)", as reported in blaberoid cockroaches other than Corydiidae ("Ectobiidae," Blaberidae, etc.) and in Mantodea; the embryos of blattoid cockroaches (Blattidae and Cryptocercidae) and Isoptera undergo blastokinesis of the "reversion type (R)," in which the anteroposterior axis of the embryo is reversed during blastokinesis. Dictyopteran blastokinesis types can be summarized as "Mantodea (N) + Blattodea [= Blaberoidea (N) + Blattoidea (R) + Isoptera (R)]".

Life-History Traits from Embryonic Development to Reproduction in the American Cockroach

“…On the posterior ventral side of the egg, a pair of blastoderm regions with higher cellular density in the lateral areas migrate medially and then fuse into an almost heart-shaped embryo. This type of embryo formation is also found in other insects in Polyneoptera, such as E. yasumatsui [ 26 ], Gryllus bimaculatus [ 30 , 31 , 32 ], Galloisiana yuasai [ 33 ] and Zorotypus caudelli [ 34 ]. This observation provides evidence for the hypothesis that embryo formation with the fusion of paired areas of higher cellular density is a potential autapomorphy of Polyneoptera.…”

“…The embryonic development period of American cockroaches was approximately 35 days under incubation at 29 °C. Based on the changes in embryonic features and referring to the embryonic development processes of Blattella germanica [ 25 ] and Eucorydia yasumatsui [ 26 ], the embryonic period of the American cockroach was divided into 20 stages.…”

Stagewise resolution of temperature-dependent embryonic and postembryonic development in the cowpea seed beetle Callosobruchus maculatus (F.)

“…Early development in C. maculatus is quite rapid as the 2-nuclei stage is reached approximately 2.5 h from oviposition at 20 °C and after 0.5 h at 32 °C. As a comparison, the time from oviposition to first cleavage varies among insects from over 1 h in rapidly developing endoparasitic wasps [38] to over 1 d in species with long life cycles such as a stonefly [41] and a cockroach [17]. The above estimates of the timing of the first cleavage differ substantially from those reported by a previous author [68] (5-6 h at 22 °C and 2 h at 30 °C).…”

Stagewise Resolution of Temperature-Dependent Embryonic and Postembryonic Development in the Cowpea Seed Beetle Callosobruchus Maculatus (F.)

“…Early development in C. maculatus is quite rapid as the 2-nuclei stage is reached approximately 2.5 h from oviposition at 20°C and after 0.5 h at 32°C. As a comparison, the time from oviposition to rst cleavage varies among insects from over 1 h in rapidly developing endoparasitic wasps [38] to over 1 d in species with long life cycles such as a stone y [41] and a cockroach [17]. The above estimates of the timing of the rst cleavage differ substantially from those reported by a previous author [68] (5-6 h at 22°C and 2 h at 30°C).…”