In 1951, eggs of Erioischia brassicae were first found in the field on 2 May, and the peak period of egg‐laying occurred 19–31 May. This was up to a month later than in the period 1948‐50.The periodic removal and examination of the surface soil showed that eggs of E. brassicae were continuously present on the host plants from mid‐June to early November. Plants under observation during this period showed an average of 285 eggs per plant and other plants exposed to attack from July to November showed an average of 162 eggs per plant. Peak periods of egg‐laying, as indicated by numbers of eggs per plant per day, occurred in late June and early July, in mid‐August and, to a less extent, in the first half of October. The plants showed no increase in the rate of infestation as the season advanced, although E. brassicae has a reproductive capacity of about 100 eggs per female and three to four generations a year.The difference between the observed egg populations and pupal populations indicated that E. brassicae had a heavy mortality rate in its immature stages. The condition of puparia showed that the species was subject to a high degree of natural control, a fact for consideration when
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