SUSCEPTIBILITY OF 1ST-INSTAR CABBAGE MAGGOT, DELIA-RADICUM (L) (ANTHOMYIIDAE, DIPTERA), TO STRAINS OF THE ENTOMOGENOUS NEMATODES STEINERNEMA-FELTIAE FILIPJEV, STEINERNEMA-BIBIONIS (BOVIEN), HETERORHABDITIS-BACTERIOPHORA POINAR, AND HETERORHABDITIS-HELIOTHIDIS (KHAN, BROOKS, AND HIRSCHMANN)

The susceptibility of first-instar cabbage maggot, Delia radicum (L.), to parasitism by seven strains or species of entomogenous nematodes was compared in Petri dishes lined with moist filter paper. The effective doses for 50% mortality (ED50) of the Mexican, Breton, and All strains of Steinernema feltiae Filipjev, of S. bibionis (Bovien), and of Heterorhabditis heliothidis (Khan, Brooks, and Hirschmann) ranged from 98 to 341 infective juveniles per host larva with overlapping 95% confidence intervals; the slopes ranged from 1.36 to 1.07. The DD136 strain of S. feltiae and the species H. bacteriophora Poinar were significantly less lethal with ED50 values of 1113 and 1719 nematodes per host larva, respectively. The addition of a thin disc of rutabaga into the test dishes increased ED50values by a factor of 20 or more. Application of the Mexican strain of S. feltiae at 5 × 105 nematodes per plant to small caged field plots of rutabaga artificially infested with eggs of D. radicum provided control similar to that with diazinon applied at 1.4 L AI per hectare. Practical control of D. radicum on rutabaga with entomogenous nematodes would require strains or species considerably more lethal than those tested here. © 1990, Entomological Society of Canada. All rights reserved.