Technical Abstract: The unique genetic phenomena responsible for inherited F1 sterility in Lepidoptera and some other arthropods also provide advantages for the use of inherited sterility instead of full sterility in a sterile insect technique (SIT) program. Lepidopteran females generally can be completely sterilized at a dose of radiation that only partially sterilizes the male of the same species. When these partially sterile males mate with fertile females, the radiation-induced deleterious effects are inherited by the F1 generation. At the appropriate dose of radiation, egg hatch is reduced and the resulting (F1) offspring are both highly sterile and predominately male. Lower doses of radiation used to induce F1 sterility increase the quality and competitiveness of the released insects. However, during a SIT program it is possible that traps used to monitor wild moth populations and over-flooding ratios (marked release males vs unmarked wild males) may capture unmarked F1 sterile males that cannot be distinguished from wild fertile males. In this study we developed a cytological technique using orcein and Giemsa stains to distinguish adult F1 progeny of irradiated males and wild males captured in traps. Our observations indicate that F1 males (sterile) from irradiated fathers can be distinguished from fertile males by the nuclei cluster in the eupyrene sperm bundles. The nuclei cluster in the fertile males exhibited a regular and organized arrangement of the sperm, whereas in F1 males the nuclei cluster of sperm was disorganized, irregular and unevenly stained.