A STUDY OF HYLEMYJTA (CHORTOPHILA) RRAS‐SICAE BOUCHE, THE CABBAGE ROOT FLU AND ITS PARASITES. WITH NOTES ON SOMX OTHER DIPTEROUS PESTS OF CRUCIFEROUS PLANTS
A detailed account is given of the life history and parasites of H. brassicae. The egg is deposited near the roots of Cruciferae, in the heads of cauliflowers, and in fall on the leaves and cut stem of Brassicas. The egg stage lasts 3-5 days. The full-grown larva is smooth and white, with a caudal corona of well-defined tubercles, 1 pair of which is bifurcate. The maggots feed in the roots of Cruciferae or in the heads of cauliflowers and turnips. Late in the fall they may occasionally be found tunnelling in the midrib of Brassica leaves. The larval period lasts 19-25 days. The puparium is reddish brown and measures about 7 mm. in length. The length of the pupal stage is very variable and may occupy 16-69 days. Pupation takes place in the soil near the plant. The adult is a dark grey insect somewhat like the house fly. There are 3 generations in the season; as a general rule hibernation is in the soil in the pupal stage. A detailed description of the parasites of H. brassicae is given the larva of the Staphylinid beetle Aleochara bilineata Gyll., the Cynipid, Cothonaspis rapae Westw., the Braconid Dacnusa stramineipes Halid., and the Anthomyid fly, Phaonia trimaculata Bouche, the larvae of which are carnivorous and feed on H. brassicae larvae. There are also described a Proctrotrupid, Exallonyx ligatus Nees., which is parasitic on the larva of Aleochara bilineata Gyll., and a Tachinid fly, Onesia agilis Meig., which is associated with H. brassicae, although the exact relationship has not been determined. An unusual form of parasitism of the adult fly by some microorganism is also figured and briefly described. Four other types of larvae found associated with those of H. brassicae in cruciferous plants are described, the most important being Phy-tomyza rufipes Meig.