Compared to micro and macroparticles, nanoparticles possess distinctive properties. Soft corals are appreciated marine sources with promising biological and chemical diversity. This study aimed to evaluate the effect of eco-friendly synthesis of Zinc oxide nanoparticles using Ovabunda macrospiculata (Om-ZnO-NPs) as an insecticidal agent. In this trial, the ultrastructural abnormalities induced in the ovaries of the housefly, Musca domestica adult females were investigated. Synthesized zinc oxide nanoparticles (ZnO-NPs) were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infra-red (FTIR) spectroscopy. Morphologically, ZnO-NPs were semi-spherical in shape with particles diameter ranging from 20.4 to 21.3 nm. Structurally, XRD data showed that ZnO-NPs were crystalline in nature. The existence of chemicals required for the reduction of zinc oxide was confirmed by FTIR spectral analysis. Data obtained showed promising larvicidal activity, where synthesized Om-ZnO-NPs showed 2-3 folds higher larval mortality percentages than the crude extract at almost all concentrations tested. The recorded LC₅₀ values were 49.061 and 22.595 ppm, while the LC₉₀ values were 91.093 and 43.393 ppm for the crude extract and Om-ZnO-NPs, respectively. Additionally, Om-ZnO-NPs severely reduced the fecundity and egg-hatchability of treated females compared to those treated with the crude extract or the untreated females. Ultrastructural investigations revealed that crude extract induced abnormalities in tested ovaries and this effect was much more pronounced in those females treated with Om-ZnO-NPs. Generally, the obtained results suggest that coral-mediated synthesis of ZnO-NPs is more feasible than the eco-friendly synthesis of ZnO-NPs with improved properties.