In a previous paper (Simmonds 1946) a curious factor affecting diapause in insects was recorded. In two species of parasitic Hymenoptera the age of the parent female at the time of oviposition has a marked effect on the tendency of the resulting larva to enter a state of diapause when full-grown. The older the female at the time of oviposition the greater is the chance that an egg will produce a larva entering diapause. In a second paper (Simmonds 1948) this maternal influence on the tendencies of her progeny to enter diapause was investigated further. Some general conclusions were drawn as to the nature of diapause, and the experiments were considered in the light of the various theories put forward to explain the phenomenon. In brief it was concluded that the underlying cause of diapause is the occurrence of a physiological disturbance at some stage in the life-history.