Testis development and dimorphic spermatogenesis in Omphisa fuscidentalis (Lepidoptera: Crambidae), an edible bamboo borer of northern Thailand

Omphisa fuscidentalis is a univoltine moth whose larvae undergo an unusually prolonged diapause (~9 months) inside bamboo internodes – a unique life‑history trait that may shape its reproductive biology. Despite its ecological and economic importance as an edible insect, little is known about its reproductive system. This study presents the first detailed analysis of testis development and sperm ultrastructure across larval, prepupal, and adult stages using light, scanning electron, and transmission electron microscopy. We describe a novel transformation from paired testes with four follicles in larvae to a fused single testis with eight follicles in the prepupal stage. Furthermore, we document sperm dimorphism in detail, highlighting structural specializations in both eupyrene and apyrene spermatozoa. Noteworthy features include micronuclei formation during apyrene spermiogenesis, a dense cap in mature apyrene sperm, a shoe‑sole-shaped mitochondrial derivative, and a developmental shift in eupyrene flagella from a hand-like to a sunshine-like configuration. These ultrastructural changes likely reflect adaptive strategies associated with diapause. By integrating multi-scale imaging, this work offers new insights into the reproductive development of O. fuscidentalis and provides a valuable reference for future comparative studies on sperm evolution and reproductive adaptations in insects with complex life cycles.