Effect of Soil Treatments of Heptachlor and Parathion on Predators and Parasites of Root Maggots Attacking Rutabagas on Prince Edward Island1

Abstract

Applications of heptachlor placed along both sides of rows of rutabagas reduced pupal parasitism of the cabbage maggot (Hylemya brassicae (Bouché)) by Aleochara bilineata (Gyll.) more than 80%. At harvest, more than twice as many root maggot pupae and only one quarter as many parasites survived in the treated as in the untreated rows. In the insecticide-free region (a band about 4 to 5 inches wide around the plants) of the treated rows, there were approximately the same numbers of root maggots as in the untreated rows; the insecticide did not appear to affect the numbers of maggots attacking the plants. A similar treatment of parathion reduced the parasitism by 23% and caused no apparent reduction in root maggot populations. When applied in a 5-ineh band in the row and just below the surface of the soil, heptachlor and parathion gave almost complete control of root maggots. The effect of such treatments on the predators and parasites has not been determined.