Do ambusher and cruiser entomopathogenic nematodes disperse differently in soil in the absence of hosts?

Eariler laboratory studies predicted dichotomy in foraging behavior of entomopathogenic nematodes (EPNs) but little is known about their dispersal in the field. We compared the lateral dispersal of a cruise foraging species, Heterorhabditis bacteriophora and an ambushing species, Steinernema carpocapsae from infected host cadavers in autoclaved soil (24% water w/w) placed in wooden arenas (0.05 m² to 1.5m²) at room temperature with and without grass. Nematode movement was estimated using Galleria mellonella baits placed in soil core samples (2 cm dia; 5 cm deep) collected in plastic cups at different time intervals (6 to 240 hr) and distances (7 to 61 cm). All experiments were repeated and replicated 5 times. Spatio-temporal data were analyzed using two-dimensional modified Fick Diffusion Model with least squares method. While, both the species exhibit nearly same average movement of infective juveniles (IJs) in soil (6 cm/day) in the absence of grass, their pattern of dispersal varied. Interestingly, nearly all H. bacteriophora IJs moved some distance away from the cadaver, most S. carpocapsae IJs remained stationary, with a small proportion moving even farther than H. bacteriophora IJs. While grass facilitated the dispersal of cruiser in soil with no insect hosts, it made no difference to ambusher’s dispersal. This study reveals remarkable innate ability of EPNs to move distances 100 times greater than their body length in a day in soil without hosts. Differences in dispersal behavior of given species may influence their distribution over the landscape which may consequently influence their use in biological pest control.