Chemical Control of the Cabbage Root Maggot Integrated with Natural Controls

Application of 5 Ibs. toxicant Ileptachlor or aldrin per acre placed in a 4- to 5-inch hand about 1½ inches below the surface of the soil in a ridged seeding drill have controlled infestations of the cabbage root maggot, Hylemya brassicae (Bouche) in cabbage and rutabagas for eight consecutive years on one farm in Prince Edward Island without detectable indications of resktance. The insecticide is so placed in the soil as to be most concentrated against the young root maggot larvae and least concentrated against the following predators and parasites: Coenosia tigrina (Fall.) and Scatophaga stercoraria. (L.), which attack and destroy H. brassicae flies in flight, on the soil surface, or on plant foliage; various species of Carabid beetles which destroy H. brassicae eggs at or near the soil surface, Trybliographa rapae (L.), the larvae of which parasitize and destroy H. brassicae larvae in the plant roots; and Aleochara bilineata (Gyll.), with adults destroying H. brassicae eggs or young larvae near the soil surface, and larvae in the plant roots, and the larvae parasitising H. brassicae puparia and destroying the pupae. Records of field observations, supplemented with data obtained on green-house determinations of the potential reproduction of both predators and host, indicate that any one of these predators could theoretically eliminate the pest population from an area in two to three generations. They do not eliminate or even give apparent economic control of the pest because a) the aerial attackers do not find and destroy adults of the pest before many eggs are deposited in the soil; b) many eggs are hidden in the soil by wind and rain and thus protected from discovery by predators; and c) larval and puparial parasites attack after the pest has injured the crop.