An Early Embryonic Diapause Stage and Developmental Plasticity in the Band-Legged Ground Cricket Dianemobius nigrofasciatus

Abstract

Egg diapause is found in a variety of insect orders and can occur in various stages, ranging from an early small germ band stage to a later stage in which an embryo exhibits appendages. Embryonic diapause is especially prominent in crickets inhabiting temperate regions, such as the band-legged ground cricket, Dianemobius nigrofasciatus. This species is common in the Japanese islands and exhibits a univoltine life cycle with obligatory egg diapause in northern regions, whereas a bivoltine life cycle with facultative egg diapause controlled by parental photoperiod and temperature is present in the southern regions. D. nigrofasciatus enters diapause during an early embryonic stage. Here we review the morphological aspects of early embryogenesis and how they relate to the various stages of diapause. By focusing on details of development, such as patterns of nuclear arrangement and the appearance of cell membranes, we can identify useful hallmarks for the study of diapause. In particular, the formation of a continuous thin layer of cells covering the egg’s surface normally reveals the formation of the cellular blastoderm. In diapause eggs, however, that continuous layer of cells covers the interior egg surface without forming a germ band, indicating that diapause occurs at the cellular blastoderm stage. Furthermore, in a bivoltine strain, diapause can be induced by low temperatures and averted by high temperatures applied to the eggs just before formation of the cellular blastoderm. In conclusion, diapause in D. nigrofasciatus entails developmental arrest at the cellular blastoderm stage, which can be influenced by temperature before blastoderm formation.