Terrestrial molluscs (Mollusca: Gastropoda) are important economic pests worldwide, causing extensive damage to a variety of crop types, and posing a health risk to both humans and wildlife. Current knowledge indicates that there are eight nematode families that associate with molluscs as definitive hosts, including Agfidae, Alaninematidae, Alloionematidae, Angiostomatidae, Cosmocercidae, Diplogastridae, Mermithidae and Rhabditidae. To date, Phasmarhabditis hermaphrodita (Schneider, 1859) Andrássy, 1983 (Rhabditida: Rhabditidae) is the only nematode that has been developed as a biological molluscicide. The nematode, which was commercially released in 1994 by MicroBio Ltd, Littlehampton, UK (formally Becker Underwood, now BASF) under the tradename Nemaslug®, is now sold in 15 different European countries. This paper reviews nematodes isolated from molluscs, with specially detailed information on the life cycle, host range, commercialization, natural distribution, mass production and field application of P. hermaphrodita.

Worldwide interest in Phasmarhabditis originates from the successful commercialisation of P. hermaphrodita as a biological control agent against molluscs in Europe. To date, P. hermaphrodita has not been isolated from South Africa and, therefore, the formulated product may not be sold locally. During a survey for mollusc-associated nematodes, P. papillosa was dissected from the slug, Deroceras reticulatum, collected from George, South Africa. The nematode was identified using a combination of morphological, morphometric, molecular and phylogenetic techniques. Virulence tests were conducted which demonstrated that P. papillosa caused significant mortality to the European invasive slug Deroceras panormitanum. Additional data are provided in the morphometrics of the infective juvenile and in the molecular identification, using the mitochondrial cytochrome c oxidase subunit I (cox1) gene. This is the first report of P. papillosa from the African continent and of its virulence against D. panormitanum.

During a survey for mollusc-associated nematodes in South Africa, a new Phasmarhabditis species was isolated from the invasive slug, Deroceras reticulatum, collected from a nursery near George in the Western Cape province. The nematode was identified using a combination of morphological, morphometric, molecular, and phylogenetic techniques. The new species, P. safricana n. sp., is characterised by the cupola-shaped tail of the female with a spike, small, non-protruding phasmids, a fingerprint-like pattern of the cuticle covering the female tail, toothlike cephalic structures of the infective juveniles, and the distinct molecular characteristics of the species. The molecular phylogeny of the new species, as inferred from its SSU and LSU rRNA gene, places P. safricana n. sp. in close proximity to P. papillosa. Virulence tests were conducted, which demonstrated that P. safricana n. sp. caused significant mortality to the European invasive slug, D. reticulatum. The new species brings the total complement of the genus to eleven species.

Summary A new species of Phasmarhabditis was isolated from the slug, Polytoxon robustum, from Nairobi, Kenya. The nematode was identified using morphological, morphometric, molecular and phylogenetic analyses. Phasmarhabditis kenyaensis n. sp. is characterised by an infective juvenile with the longest body length in the genus, measuring 1232 (1107-1336) μm, by the presence of males with a bursa bearing nine bilateral pairs of genital bursal papillae and one pair of papilliform phasmids flanking the tail, cephalate paired spicules, with an arc length of 71 (57-81) μm, as well as by females with a vulva located at the mid-body region and a conoid tail shape, with two phasmids located at ca 40% of the tail length. The molecular phylogeny of the new species, as inferred from its SSU (small subunit) rRNA gene, places P. kenyaensis n. sp. genetically close to undescribed phasmarhabditids from South Africa, suggesting an African grouping, while the D2-D3 (large ribosomal subunit) and ITS region analyses relate P. kenyaensis n. sp. to P. meridionalis, with weak bootstrap support. This is the third new Phasmarhabditis species described from the African continent, the new species bringing the total known complement of the genus to 14 species. A morphometric compendium to all species cultured in vivo is supplied.

Summary In the period from August to October 2018, 140 specimens of the Spanish slug, Arion vulgaris, were collected from Podbrezje, Slovenia. Slugs were dissected and examined for the presence of parasitic nematodes within the cadavers. Identification of the nematodes was conducted using morphological and molecular techniques and confirmed the presence of Phasmarhabditis papillosa. This is the first record of P. papillosa from the mollusc host, A. vulgaris. Laboratory experiments aimed at testing the efficacy of P. papillosa against A. vulgaris were conducted using nematodes grown in vivo. Nematodes were applied at concentration rates of 50, 100 and 200 nematodes slug−1, respectively. Three weeks following treatment, the mortality of slugs was confirmed in all treatments (50 nematodes slug−1, 37.4 ± 2.7%; 100 nematodes slug−1, 48.4 ± 2.7%; 200 nematodes slug−1, 50.6 ± 2.7%). However, the pathogenesis of P. papillosa was observed first in the treatments with the lowest nematode dose at 4 days after treatments, while a decrease in the feeding behaviour of slugs was noted first in the treatments with the highest nematode dose. Future opportunities for the potential use of P. papillosa as a biological control agent against slugs are discussed. This is the first report of P. papillosa from Slovenia, and of its virulence against A. vulgaris.