OBSERVATIONS ON THE BIOLOGY and CONTROL OF CABBAGE ROOT FLY, ERIOISCHIA BRASSICAE (BCHE)

Abstract

In the south‐east of England egg‐laying by Erioischia brassicae Bche began in the third week of April and was at its maximum in the fourth week of April and the first week of May. From then on to early October small numbers of eggs were continually present about brassica crops. Egg counts on cauliflowers at the end of April showed up to 141 eggs/plant and on spring cabbage on 6 May up to 117 eggs; the flies showed no preference for newly set plants. Eggs on the soil were almost exclusively those of Erioischia brassicae; eggs on the plants were mainly those of Pegohylemyia fugax Meig., with small numbers of Erioischia brassicae and Delia cilicrura Rond.Larvae were found continuously from the fourth week of April to mid‐January, those found in December and January were from the previous autumn. Larvae, up to eighty‐one per plant, at the roots of brassica crops were almost exclusively Erioischia brassicae. A few Pegohylemyia fugax and Delia cilicrura occurred, but no Erioischia floralis Fall, were found. A technique for separating larvae from the soil and plant roots is described.Great variation in the size of puparia was noted. Small puparia (4‐4‐5 mm. long) were heavily parasitized by cynipid wasps.In trials on cauliflowers and brussels sprouts the efficiency of calomel dust (4 %) and benzene hexachloride (flea beetle and wireworm dusts) was compared. An application of B.H.C. wireworm dust at 40 lb./acre (approximately 11,000 plants) appeared to have the same efficiency as an application of calomel dust at the rate of 80 lb./acre. The concentration of benzene hexachloride in flea beetle dust applied at rates up to 40 lb./acre (11,000 plants) was insufficient to secure the measure of control given by calomel dust at 80 lb./acre. In 1949 calomel dust remained effective from 2 July, when it was applied, until 30 August when observations ceased.Good growing conditions masked injury and were very important in preventing loss from injury by cabbage root fly.