Mortality of the invasive white garden snail Theba pisana exposed to three US isolates of Phasmarhabditis spp (P. hermaphrodita, P. californica, and P. papillosa).

Theba pisana is a serious snail pest in many parts of the world and affects diverse crops including grain, vegetables, grapevines, and ornamental plants and shrubs. Due to its gregarious nature, ability to reproduce rapidly, and the difficulty of controlling it by conventional methods, it has the potential to become a significant pest where introduced. Mitigating this pest is an important challenge that must be addressed. Phasmarhabditis hermaphrodita, is a gastropod-killing nematode that is commercially available only in Europe (Nemaslug ®) and Sub-Saharan Africa (Slugtech ® SP). The use of effective gastropod-killing nematodes in the genus Phasmarhabditis (P. hermaphrodita, P. californica and P. papillosa) in California may provide one strategy for alleviating the potential damage and further spread of these snails, which are currently limited to San Diego and Los Angeles counties. Laboratory assays demonstrated for the first time that US isolates of P. hermaphrodita, P. californica and P. papillosa at 150 DJs/cm2 caused significant mortality and are equally lethal to T. pisana. Molluscicidal efficacy of these nematodes are comparable with those of iron phosphate, at the recommended high dose of 4.88 kg/m2. Additional trials are needed to determine their effects at lower dose and whether they are dependent on the size or age of the snails

Lethality of Phasmarhabditis spp. (P. hermaphrodita, P. californica, and P. papillosa) Nematodes to the Grey Field Slug Deroceras reticulatum on Canna Lilies in a Lath House

The grey field slug, Deroceras reticulatum, is an agricultural pest causing damage to a wide variety of crops each year. The nematode Phasmarhabditis hermaphrodita has been shown to effectively kill this slug in field-simulated conditions, leading to its widespread use as a biological control agent in Europe. However, recently discovered isolates of Phasmarhabditis from California have not been tested in a field-simulated environment. The lethality of three local isolates of Phasmarhabditis (P. hermaphrodita, P. californica, & P. papillosa) as well as the molluscicide Sluggo Plus® was assessed on D. reticulatum in a lath house. Remaining leaf area on Canna lilies and slug mortality were recorded after 3 weeks of exposure to treatments. Local isolates efficiently killed D. reticulatum and protection from leaf damage was attained by treatment with P. papillosa. Further experimentation is required to assess plant protection afforded by Phasmarhabditis as plants in some trials may have been in poor health. The three tested Phasmarhabditis isolates are reasonable candidates for biological control within the United States but additional information, particularly on the lethality to non-target gastropods, is needed before an informed decision on their use can be made

A Study of the Distribution, Pathogenicity, and Native Microbiome of Three US Strains of Phasmarhabditis (P. californica, P. hermaphrodita, and P. papillosa)

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

Lethality of Three <i>Phasmarhabditis</i> spp. (<i>P. hermaphrodita</i>, <i>P. californica</i>, and <i>P. papillosa</i>) to Succinea Snails

Succinea snails are considered to be invasive and pestiferous gastropods to those in the floricultural industry. Their small size makes them difficult to locate within large plant shipments, and their presence on decorative plants can constitute for an entire shipment to be rejected for sale and distribution. Research performed on Succinea snails is limited, especially in terms of effective mitigation strategies. The nematode Phasmarhabditis hermaphrodita is a biological control agent used on pestiferous gastropods throughout some European nations. Here, three strains of Phasmarhabditis from the United States (P. hermaphrodita, P. californica, and P. papillosa) were assessed as biological control agents against Succinea snails in controlled laboratory conditions, along with the molluscicide Sluggo Plus® as a control. All species of Phasmarhabditis applied at 30 IJs/cm2 caused significant mortality compared to the non-treated control and treatment with Sluggo Plus®. P. californica caused 100% mortality 6 days after exposure, while P. hermaphrodita and P. papillosa caused the same mortality rate 7 days after exposure. The molluscicide was unable to cause significant mortality compared to the non-treated control. Additional research with US Phasmarhabditis strains, including their non-target effects and distribution may lead to their being a viable option for biological control against Succinea snails

Dose dependence of Phasmarhabditis isolates (P. hermaphrodita, P. californica, P. papillosa) on the mortality of adult invasive white garden snails (Theba pisana).

Theba pisana is an invasive snail pest which has established itself in San Diego County and some areas of Los Angeles County, California. The snail has grown to large populations in some areas and mitigation is becoming necessary to stop the spread of the species. In a previous study, three US strains of Phasmarhabditis species (P. californica, P. papillosa, and P. hermaphrodita) effectively killed juvenile (0.25 gram each, 4-6 mm wide) T. pisana in laboratory conditions at 5 times (150 IJs/cm2) the recommended dose. Based on laboratory assays, we demonstrated that the same three US strains of Phasmarhabditis can effectively kill larger adult T. pisana (0.4-1.2 gram, 11.5-15mm wide) in two weeks at the same dose. The strains were more efficient at killing T. pisana than the compared molluscicide Sluggo Plus®. Results further showed that the most virulent P. californica did not effectively kill T. pisana at lower doses of 30 IJs/cm2 and 90 IJs/cm2. Additional research is needed to develop the most efficient means of application of Phasmarhabditis to mitigate T. pisana in the field

Dose dependence of Phasmarhabditis isolates (P. hermaphrodita, P. californica, P. papillosa) on the mortality of adult invasive white garden snails (Theba pisana).

Theba pisana is an invasive snail pest which has established itself in San Diego County and some areas of Los Angeles County, California. The snail has grown to large populations in some areas and mitigation is becoming necessary to stop the spread of the species. In a previous study, three US strains of Phasmarhabditis species (P. californica, P. papillosa, and P. hermaphrodita) effectively killed juvenile (0.25 gram each, 4-6 mm wide) T. pisana in laboratory conditions at 5 times (150 IJs/cm2) the recommended dose. Based on laboratory assays, we demonstrated that the same three US strains of Phasmarhabditis can effectively kill larger adult T. pisana (0.4-1.2 gram, 11.5-15mm wide) in two weeks at the same dose. The strains were more efficient at killing T. pisana than the compared molluscicide Sluggo Plus®. Results further showed that the most virulent P. californica did not effectively kill T. pisana at lower doses of 30 IJs/cm2 and 90 IJs/cm2. Additional research is needed to develop the most efficient means of application of Phasmarhabditis to mitigate T. pisana in the field

Mortality of the invasive white garden snail Theba pisana exposed to three US isolates of Phasmarhabditis spp (P. hermaphrodita, P. californica, and P. papillosa).

Theba pisana is a serious snail pest in many parts of the world and affects diverse crops including grain, vegetables, grapevines, and ornamental plants and shrubs. Due to its gregarious nature, ability to reproduce rapidly, and the difficulty of controlling it by conventional methods, it has the potential to become a significant pest where introduced. Mitigating this pest is an important challenge that must be addressed. Phasmarhabditis hermaphrodita, is a gastropod-killing nematode that is commercially available only in Europe (Nemaslug ®) and Sub-Saharan Africa (Slugtech ® SP). The use of effective gastropod-killing nematodes in the genus Phasmarhabditis (P. hermaphrodita, P. californica and P. papillosa) in California may provide one strategy for alleviating the potential damage and further spread of these snails, which are currently limited to San Diego and Los Angeles counties. Laboratory assays demonstrated for the first time that US isolates of P. hermaphrodita, P. californica and P. papillosa at 150 DJs/cm2 caused significant mortality and are equally lethal to T. pisana. Molluscicidal efficacy of these nematodes are comparable with those of iron phosphate, at the recommended high dose of 4.88 kg/m2. Additional trials are needed to determine their effects at lower dose and whether they are dependent on the size or age of the snails