The parasitic nematode Phasmarhabditis hermaphrodita defends its slug host from being predated or scavenged by manipulating host spatial behaviour

Abstract

Infective stages of commercially used molluscicidal rhabditide nematodes Phasmarhabditis hermaphrodita contain bacterial symbionts which kill their host by septicaemia. The nematodes feed on the multiplying bacteria and entire host tissue, develop and repeatedly reproduce. Invertebrate cadavers are rapidly (from minutes to hours) removed by scavengers. However nematodes need days to complete their life cycle inside the host. The post mortem locations of slugs killed by six different treatments (three types of molluscicides, a simulation of unsuccessful predation and two P. hermaphrodita nematode treatments) were compared. In comparison to other pathogenic states, significantly more slugs killed by the nematodes died within the soil, where the scavenging pressure is weaker than on the soil surface (where most of the slugs died regardless treatment). We suggest that this is an outcome of behavioural manipulation, which prevent the parasites from being predated or scavenged together with their host until the nematodes complete development inside the host cadaver.