Juvenile hormone analog, fenoxycarb induced apoptotic effects in the developing ovary of Daphnia magna.

Juvenile hormone analogs (JHAs) are widely used insect growth regulators that disrupt endocrine signaling and impair reproduction in arthropods. Although their effects on non-target crustaceans such as Daphnia magna are well documented, the cellular mechanisms underlying JHA-induced reproductive toxicity remain unclear. In this study, we performed time-course exposure experiments to identify the sensitive window during which fenoxycarb reduces fecundity and investigated the associated ovarian changes. We generated a germline-specific VASA:H2B-GFP knock-in line to visualize ovarian nuclei in vivo and found that exposure during 16-32 h after oviposition resulted in marked reductions in offspring number. High-resolution fluorescence and multiphoton imaging revealed apoptosis-like nuclear abnormalities in developing oocytes, indicating that oocyte degeneration contributes to reduced fecundity. This study provides evidence that oocyte degeneration contributes to fenoxycarb-induced reproductive impairment and highlights the utility of genetic and live-imaging tools for advancing mechanistic understanding of endocrine disruption in small aquatic invertebrates.