Phylogenetic evidence for the invasion of a commercialized European Phasmarhabditis hermaphrodita lineage into North America and New Zealand

Abstract

Biological control (biocontrol) as a component of pest management strategies reduces reliance on synthetic chemicals, and seemingly offers a natural approach that minimizes environmental impact. However, introducing a new organism to new environments as a classical biocontrol agent can have broad and unanticipated biodiversity effects and conservation consequences. Nematodes are currently used in a variety of commercial biocontrol applications, including the use of Phasmarhabditis hermaphrodita as an agent targeting pest slug and snail species. This species was originally discovered in Germany, and is generally thought to have European origins. P. hermaphrodita is sold under the trade name Nema-slug®, and is available only in European markets. However, this nematode species was discovered in New Zealand and the western United States, though its specific origins remained unclear. In this study, we analyzed 45 nematode strains representing eight different Phasmarhabditis species, collected from nine countries around the world. A segment of nematode mitochondrial DNA (mtDNA) was sequenced and subjected to phylogenetic analyses. Our mtDNA phylogenies were overall consistent with previous analyses based on nuclear ribosomal RNA (rRNA) loci. The recently discovered P. hermaphrodita strains in New Zealand and the United States had mtDNA haplotypes nearly identical to that of Nemaslug®, and these were placed together in an intraspecific monophyletic clade with high support in maximum likelihood and Bayesian analyses. We also examined bacteria that co-cultured with the nematode strains isolated in Oregon, USA, by analyzing 16S rRNA sequences. Eight different bacterial genera were found to associate with these nematodes, though Moraxella osloensis, the bacteria species used in the Nemaslug® formulation, was not detected.

Size-susceptibility of Cornu aspersum exposed to the malacopathogenic nematodes Phasmarhabditis hermaphrodita and P. californica

“…The three strains of P. californica used in this study were isolated from one single snail (O. draparnaudi) (Andrus & Rae, 2019). This highlights how strains isolated in close proximity to each other and phylogenetically similar (Howe et al, 2020) differ in their pathogenic abilities (Cutler & Rae, 2020) as well as host seeking abilities (Andrus et al, 2018). Therefore, in order to produce and develop a suitable biological control agent for slugs and snails, intraspecific variation of strains should be investigated.…”

“…For example, Cutler and Rae (2020) reported that several wild strains of P. hermaphrodita were more virulent to slugs (Deroceras invadens) than the commercial strain and other wild strains. It should be noted that these P. hermaphrodita strains were isolated from separate slugs from different areas around Liverpool and are genetically distinct (Howe et al, 2020). The three strains of P. californica used in this study were isolated from one single snail (O. draparnaudi) (Andrus & Rae, 2019).…”

A Literature Review of Biological and Bio-Rational Control Strategies for Slugs: Current Research and Future Prospects

“…In-depth studies on each of these slugparasitic nematodes should be conducted to evaluate their effect on nontarget organisms, the post-application survival rate and suitable production technology. Their pathogenicity should also be tested against a wide variety of slug species, including nonpestiferous native and protected gastropods, the understanding of which is particularly important in countries outside Europe, where restrictions have been imposed over the use of P. hermaphrodita [125].…”

Terrestrial Slugs in Neotropical Agroecosystems

“…Nematodes and pathogens of slugs are also of interest for slug biological control efforts worldwide. The nematode Phasmarhabditis hermaphrodita (Schneider, 2016) is available commercially in Europe (Pieterse et al, 2016), and has been recently introduced to several countries (Howe et al, 2020). In the Neotropics, Mermithid and Rhabditid nematodes have been found parasitizing slugs (Thiengo, 1995;Posada-Flórez et al, 2001;Rueda et al, 2002;Moreno Suárez et al, 2008).…”