Embryonic Development of Appasus japonicus Vuillefroy, With Special Reference to Mouthparts Formation (Insecta: Heteroptera, Belostomatidae)

The order Hemiptera s. lat. (=Homoptera + Heteroptera), comprising approximately 140 families and 70,000 species, is the largest order among hemimetabolous insects in terms of species diversity. A key trait shared among these insects is their specialized piercing-sucking mouthparts, which have been considered an important factor in their diversification. However, knowledge of how these characteristic hemipteran mouthparts form during embryogenesis remains limited and biased toward model species. In this study, we observed the embryonic development of the heteropteran insect Appasus japonicus (Belostomatidae). We divided its embryonic development into 10 stages and provided a detailed description. Additionally, we examined its developmental processes and compared them with the embryogenesis of closely related groups. As a result, we confirmed that (1) the maxillary plate, one of the structures forming the heteropteran mouthparts, is homologous to the maxillary palp, and (2) most parts of the stylet-like mandibles and maxillae are housed within the labial palp.