Rate of lateral movement of entomopathogenic nematodes Heterorhabditis bacteriophora and Steinernema carpocapsae from infected host cadavers in soil

The dispersal ability and unique foraging strategies of entomopathogenic nematodes, Heterorhabditis bacteriophora (cruiser) and Steinernema carpocapsae (ambusher) in soil, are the key factors which play a role in their effectiveness as biocontrol agents for soil inhabiting insect pests. The rate of lateral dispersal of Heterorhabditis bacteriophora GPS11 strain from infected host cadavers was quantified in 5 cm deep autoclaved soil with 24% moisture content placed in wooden trays at room temperature (21°C). Three experiments with different sized trays: 22.86 cm x 22.86 cm, 61 cm x 61 cm and 122 cm x 122 cm were conducted. Each experiment was replicated five times and repeated. A single 10-day old cadaver of final instar Galleria mellonella infected with H. bacteriophora was placed in the center of each tray. Soil core samples (2 cm dia and 5 cm deep) were collected in plastic cups at different intervals from 6 to 240 hours and at different distances from 3.81 to 61 cm from the cadaver and an uninfected G. mellonella larva was placed in each cup to examine nematode infection three days later. The spatio-temporal data were analyzed by a two-dimensional modified Fick Diffusion Model with least squares method. Average movement of infective juveniles was 6 cm/day. Number of infective juveniles moving a given distance declined with increasing distance from the cadaver with 40% traveling >15 cm and 2.5% traveling >60 cm in 240 hours. This study revealed remarkable innate ability of H. bacteriophora to move in soil in the absence of a host. Experiments with Steinernema carpocapsae ALL strain are currently in progress.