Phasmarhabditis hermaphrodita as a Control Agent for Slugs

Abstract

While there has been intense study on entomopathogenic nematodes (EPNs) by numerous research groups throughout the world, there has been much less work on nematodes that can control slugs. A survey of academic research papers listed in the Scopus database in December 2014 using the search terms “Steinernema or Heterorhabditis” revealed over 2,100 hits compared with a mere 82 hits for “Phasmarhabditis”. Conversely, while the EPNs have a relatively recent history, with the first Steinernema spp. being described in 1923 (Steiner, 1923), Phasmarhabditis hermaphrodita Schneider (Rhabditida: Rhabditidae) was first described as a parasite of slugs in 1859 (Schneider, 1859). The slug parasitic nematode, P. hermaphrodita featured prominently in Maupas’ classic paper on nematode reproduction (Maupas, 1900). This paper is best known for including the original description of Caenorhabditis elegans Maupas (Rhabditida: Rhabditidae) but the paper also contained drawings, measurements, and experimental observation on the reproduction of P. hermaphrodita which Maupas called Rhabditis caussaneli. However, there was virtually no more work done on this nematode until its potential for commercialisation as a bio–pesticide was first realised, and published as a patent (Wilson, Glen, & Pearce, 1993). The lifecycle of P. hermpahrodita is similar in many ways to EPNs (Table 21.1). The infective stage is a dauer larva that penetrates slugs through the dorsal integumental pouch (Wilson, Glen, & George, 1993; Tan & Grewal, 2001a). Larvae feeding within the slug develop into adults and eventually kill the host within 4–21 days. However, there are certain key differences from EPNs, most notably that P. hermaphrodita is a facultative parasite that can reproduce on a wide range of substrates including slug faeces, dead earthworms, dead insects, compost and leaf litter (Tan & Grewal, 2001a; MacMillan et al., 2009; Nermuť, Půža, & Mracek, 2014). But apart from this basic understanding, we have very little knowledge of the nematode’s biology and ecology.