All female broods in field and laboratory populations of the egyptian cotton leafworm Spodoptera littoralis (Lepidoptera Noctuidae).

Egg-batches of S. littoralis (Boisd.) collected in Crete Greece showed an abnormal sex ratio; 24% yielded predominantly female adults.The field data and data from 9 generations of a laboratory strain, which produced predominantly female offspring, showed that this abnormal condition was transmitted between generations by the females. The mean percentage hatch of egg-batches collected from the field which produced females only was 59.6 and the mean percentage hatch of the eggs of the laboratory strain was 58.8. Production of females only is a result of the mortality of the male embryos. Occasionally, abnormal females from the laboratory strain reverted to producing offspring of both sexes. This recovery from the abnormal condition became more common as successive generations were bred in the laboratory. One female of a normal strain produced all-female offspring and descendants of this female were similarly affected. The females of the unisexual laboratory strain were similar in appearance to normal females, but laid significantly smaller egg-batches.