Dispersal patterns and behaviour of the nematode Phasmarhabditis hermaphrodita in mineral soils and organic media

The commercially available parasitic nematode Phasmarhabditis hermaphrodita is an effective biocontrol agent for slugs and particularly Deroceras reticulatum, a widespread pest species. Use of the nematode is currently limited by cost and it may be that by developing a fuller understanding of the ecology and behaviour of this nematode, more cost effective application strategies can be developed. We investigated the ability of two strains of P. hermaphrodita (one newly isolated and one that had been maintained in vitro for >15 years) to move through mineral soils and organic media. Active dispersal of both strains was found to be greatest in organic media (bark chips and leaf litter, and to a lesser extent peat) and the nematode was capable of growth and reproduction in leaf litter. Conversely, active dispersal was poor in mineral soils. Nematodes moved further in a clay loam compared with a sandy loam, and moved more at a bulk density of 1.0 vs. 1.2 Mg m⁻³. However, P. hermaphrodita was capable of moving greater distances in mineral soils by using the earthworm Lumbricus terrestris as a phoretic host. Our data suggest that P. hermaphrodita is a facultative parasite that is adapted to living in leaf litter and organic material where slugs frequently rest. The implications of these findings for using the nematode as a biological control agent for slugs are discussed.