Steinernema boemarei n. sp. (Nematoda: Steinernematidae), a new entomopathogenic nematode from southern France

STEINERNEMA ADAMSI N. SP. (RHABDITIDA: STEINERNEMATIDAE), A NEW ENTOMOPATHOGENIC NEMATODE FROM THAILAND

A new species of entomopathogenic nematode, Steinernema adamsi n. sp., was recovered from the soil of a longan tree (Dimocarpus sp.) in Mueang Lamphun District, Thailand, using baiting techniques. Upon analysis of the nematode's morphological traits, we found it to be a new species of Steinernema and a member of the Longicaudatum clade. Molecular analyses of the ITS rDNA and D2D3 of 28S rDNA sequences further confirmed that S. adamsi n. sp. is a new species of the Longicaudatum clade, which is closely related to Steinernema guangdongense and Steinernema longicaudam. Using morphometric analysis, the infective juveniles measure between 774.69 and 956.96 μm, males have a size range of 905.44 to 1,281.98 μm, and females are within the range of 1,628.21 to 2,803.64 μm. We also identified the symbiotic bacteria associated with the nematode based on 16S sequences as Xenorhabdus spp. closely related toXenorhabdus griffiniae. Furthermore, we have successfully assessed a cryopreservation method for the long-term preservation of S. adamsi n. sp. Successful cryopreservation of this new species will allow for the longer preservation of its traits and will be valuable for its future use. The discovery of this new species has significant implications for the development of effective biological control agents in Thailand, and our work contributes to our understanding of the diversity and evolution of entomopathogenic nematodes.

Steinernema khuongi n. sp. (Panagrolaimomorpha, Steinernematidae), a new entomopathogenic nematode species from Florida, USA

In this study, molecular (ribosomal sequence data), morphological and cross-hybridization properties were used to identify a new Steinernema sp. from Florida, USA. Molecular and morphological data provided evidence for placing the novel species into Clade V, or the 'glaseri-group' of Steinernema spp. Within this clade, analysis of sequence data of the rDNA genes, 28S and internal transcribed spacer (ITS), depicted the novel species as a distinctive entity and closely related to S. glaseri and S. cubanum. Additionally, cross-hybridization assays showed that the new species is unable to interbreed with either of the latter two species, reinforcing its uniqueness from a biological species concept standpoint. Key morphological diagnostic characters for S. khuongi n. sp. include the mean morphometric features of the third-stage infective juveniles: total body length (average: 1066 μm), tail length (average: 65 μm), location of the excretory pore (average: 80.5 μm) and the values of c (average: 16.4), D% (average: 60.5), E% (average: 126) and H% (average: 46.6). Additionally, males can be differentiated from S. glaseri and S. cubanum by the values of several ratios: D% (average: 68), E% (average: 323) and SW% (average: 120). The natural distribution of this species in Florida encompasses both natural areas and citrus groves, primarily in shallow groundwater ecoregions designated as 'flatwoods'. The morphological, molecular, phylogenetic and ecological data associated with this nematode support its identity as a new species in the S. glaseri-group.

Characterisation of the dimorphic Deladenus beddingi n. sp. and its associated woodwasp and fungus

A new dimorphic species of Deladenus isolated from Sirex californicus from Washington, USA, is described as D. beddingi n. sp. Evolutionary relationships of the new species with other Deladenus species were assessed using multilocus sequencing. Phylogenetic relationships derived from analyses of mtCO1 and ITS showed D. beddingi n. sp. to be genetically distinct from other North American Deladenus parasitising Sirex. Molecular analyses indicated that D. beddingi n. sp. is a member of the D. siricidicola species complex, which also includes undescribed native Deladenus from Sirex cyaneus and S. nitidus, and D. siricidicola from S. noctilio. Mycophagous adults were characterised by the position of the excretory pore, which was located 32 (22-52) and 48 (38-69) μm anterior to the hemizonid in mycophagous females and males, respectively. Typologically, the new species is most similar to D. siricidicola, D. proximus and D. nitobei, but can be distinguished from these species by several morphometric traits, including the value of ratios a, b, c of the mycophagous females and males, ratio b of the infective females, and the morphology of the tail of the mycophagous females, which is narrow and gradually tapering. This novel nematode species feeds on the fungus Amylostereum chailletii during its mycophagous phase. Experimental results showed very little reproduction by D. beddingi n. sp. when feeding on A. areolatum compared to robust reproduction when feeding on A. chailletii.

Steinernema litchii n. sp. (Rhabditida: Steinernematidae), a new entomopathogenic nematode from South Africa

During a survey in the Mpumalanga province of South Africa, aSteinernemaspecies was isolated from a soil sample taken from a litchi orchard.Steinernema litchiin. sp. can be separated from other, closely related, species in theglaseri-group by morphological, morphometric and molecular analyses. The infective third-stage juvenile of the new species has a body length of 1054 (953-1146) μm, distance from head to excretory pore of 78 (64-86) μm, as well as eight ridges (i.e., nine lines) in the mid-body region. The c-ratio of 10 (9-13) is low and the tail is long at 95 (73-105) μm. First generation males have a spicule length of 86 (76-96) μm and a gubernaculum length of 65 (59-72) μm. The tail of the first generation male lacks a mucron; that of the second generation always bears one. The genital papillae total 23 and consist of 11 pairs and an unpaired precloacal papilla. The vulva ofS. litchiin. sp. has a slightly asymmetrical protuberance and short, double-flapped epiptygmata. The female has a slightly protuberant postanal swelling. Phylogenetic analysis of the internal transcribed spacer (ITS) and of the 28S (D2-D3) regions of the ribosomal DNA (rDNA) confirmed the close relationship ofS. litchiin. sp. to theKarii-clade. Both morphological and molecular evidence support the species status ofS. litchiin. sp.

Steinernema innovationi n. sp. (Panagrolaimomorpha: Steinernematidae), a new entomopathogenic nematode species from South Africa

Morphological and molecular sequence data were combined with cross-hybridization studies and used to identify a new Steinernema sp. from Free State, South Africa. Molecular and morphological data indicate that the new species belongs to the 'glaseri-group' of Steinernema spp. Key morphological diagnostic characters for S. innovationi n. sp. include the morphometric features of the third-stage infective juveniles: total body length = 1054 (1000-1103) μm, tail length = 108 (97-117) μm, location of the excretory pore = 88 (82-91) μm, and D% = 58 (54-63), E% = 115 (104-137) and H% = 43 (37-46). Additionally, the morphology of the spicules and gubernaculum of the first-generation males are considered key diagnostic traits. Steinernema innovationi n. sp. was also characterized by analysis of both rDNA and mitochondrial gene sequence data, which further indicate the uniqueness of this Steinernema species.

The xnp1 P2-like tail synthesis gene cluster encodes xenorhabdicin and is required for interspecies competition

Xenorhabdus nematophila, the mutualistic bacterium of the nematode Steinernema carpocapsae, produces the R-type bacteriocin called xenorhabdicin, which is thought to confer a competitive advantage for growth in the insect host. We have identified a P2-like tail synthesis gene cluster (xnp1) that is required for xenorhabdicin production. The xnp1 genes were expressed constitutively during growth and were induced by mitomycin C. Deletion of either the sheath (xnpS1) or fiber (xnpH1) genes eliminated xenorhabdicin production. Production of R-type bacteriocins in a host organism had not been shown previously. We show that xenorhabdicin is produced in the hemocoel of insects infected with the wild type but not with the ΔxnpS1 deletion strain. Xenorhabdicin prepared from the wild-type strain killed the potential competitor Photorhabdus luminescens TT01. P. luminescens was eliminated during coculture with wild-type X. nematophila but not with the ΔxnpS1 strain. Furthermore, P. luminescens inhibited reproduction of S. carpocapsae in insect larvae, while coinjection with wild-type X. nematophila, but not the ΔxnpS1, strain restored normal reproduction, demonstrating that xenorhabdicin was required for killing P. luminescens and protecting the nematode partner. Xenorhabdicin killed X. nematophila from Steinernema anatoliense, demonstrating for the first time that it possesses intraspecies activity. In addition, activity was variable against diverse strains of Xenorhabdus and Photorhabdus and was not correlated with phylogenetic distance. These findings are discussed in the context of the role of xenorhabdicin in the life cycle of the mutualistic bacterium X. nematophila.