Vertical Migration of Heterorhabditis bacteriophora and H. heliothidis (Nematoda: Heterorhabditidae) in Sandy Loam Soil.

The entomogenous nematodes Heterorhabditis bacteriophora Poinar and H. heliothidis (Khan, Brooks, and Hirschmann) and their associated bacterium Xenorhabdus luminescens (Poinar and Thomas) have been tested against a humher of insect pests with some encouraging results (11). Simons (14) obtained 90% control of tile black vine weevil, Otiorhynchus sulcatus Fab., after applying Heterorhabditis sp. to the soil surface in greenhouses. Similar results were reported by Bedding and Miller (1) and Georgis et al. (7) using H. heliothidis. Laboratory tests using H. heliothidis against Mediterranean fruit fly adults, Ceratitis capitat (Wied.), gave 85% control (12). Recently, confined field tests showed that the application of H. bacteriophora to brussels sprout seedlings have protected 88% of the plants from damage caused by the cabbage root maggot, Hylemya brassicae (Weld.) (8). If these nematodes are to be used as biological control agents, then more information is needed regarding their ability to move in soil. T h e present study defines the migration of H. bacteriophora and H. heliothidis in sandy loam soil under laboratory conditions, Heterorhabditis bacteriophora and H. heliothidis were cultured separately in larvae of the greater wax moth Galleria mellonella L. (13). After extraction, infective juveniles were stored in water for 3 weeks at 8-10 C. Vertical migration of H. bacteriophora and H. heliothidis juveniles was studied in sandy loam soil (10% clay, 10% silt, 80% sand). T h e soil had been steam sterilized and treated with 30 ml of distilled water per 100 cc soil. Vertical columns 10 cm in length consisting of 2-cm sections of plastic tubing