UC Riverside

Phasmarhabditis hermaphrodita, a gastropod specific facultative parasite, has been used as a successful biological control agent across Europe under the brand name Nemaslug®. However, Phasmarhabditis nematodes have not been permitted for use in the United States since that they had not been found locally within the country. We surveyed nurseries and garden centers throughout California and identified local populations of Phasmarhabditis including Phasmarhabditis californica, P. hermaphrodita, Phasmarhabditis papillosa, and another close relative to P. papillosa. We also described the hosts which the nematodes were found in. P. hermaphrodita and P. californica seem to share an environmental niche in Northern and Central California while P. papillosa was only found in Southern California. We also tested the pathogenicity of the discovered local Phasmarhabditis strains against the invasive snail Theba pisana. The assays were performed to assess the efficacy of the strains as biological control agents. All tested strains caused significant mortality against adult T. pisana at five times the Nemaslug® recommended dose (150 IJs/cm2 ). Upon further assessment using only P. californica, it was found that the strain was not capable of causing an economically significant amount viii of mortality to T. pisana at the recommended rate (30 IJs/cm2 ) or at three times the recommended rate (90 IJs/cm2 ). Lastly, we decided to assess the native microbiome of local Phasmarhabditis isolates discovered during our surveys. The microbiome of the gastropod specific parasites is not well studied. Our surveys presented great opportunities for us to explore their microbiomes across a large geographic region in their natural habitats. The microbiome assessments were performed via 16S sequencing of Phasmarhabditis nematodes freshly identified from gastropod cadavers. We found that their microbial community was influenced by nematode species, location, and gastropod host from which the nematode was collected. The predominant bacteria of the isolates included Shewanella, Clostridium perfringens, Aeromonadaceae, Pseudomanodaceae, and Acinetobacter, with some nematode species having more frequent associations with certain bacterial species than others. These discoveries on the local strains of Phasmarhabditis support the possibility of these nematodes as a biological control option within the United States.