Lateral movement of the entomopathogenic nematode Heterorhabditis bacteriophora in soil under laboratory conditions

Despite the growing importance of entomopathogenic nematodes as biocontrol agents for soil inhabiting insect pests, little is known of their population and spatial ecology. In a series of three consecutive laboratory experiments, the horizontal movement of Heterorhabditis bacteriophora GPS11 strain was quantified in 5 cm deep autoclaved soil with 24% moisture content placed in three different sized arenas (22.86 cm x 22.86 cm, 61 cm x 61 cm, and 122 cm x 122 cm) at room temperature (21°C). A single 10-day old cadaver of fourth instar Galleria mellonella infected with H. bacteriophora was placed in the center of each arena and the movement of at least one nematode from it to site of the soil sample, collected in small cups with soil core samples (2 cm in diameter) at intervals from 6 to 240 hours and at distances from 7 to 61 cm from the center, was inferred from death of the bait (one uninfected G. mellonella larva per cup) three days later. Each of the three arena sizes were replicated five times and all three experiments were repeated with similar sampling distances and time intervals. The data collected comprised the proportion of dead G. mellonella baits at 96 combinations of distance and time computed from 5 – 10 replicates. A two-dimensional modified Fick diffusion model was fit to the spatio-temporal data by least squares method and descriptive statistics calculated. The average movement of infective juveniles in soil was 6 cm/day. The 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 up to 240 hours. This study has shown that the dispersal ability of H. bacteriophora in soil with no source of attraction in the form of bait or carbon dioxide from other organisms.G054