Nematology, 2007, Vol. 9(3), 379-396 Steinernema texanum n. sp. (Rhabditida: Steinernematidae), a new entomopathogenic nematode from Texas, USA Khuong B. NGUYEN 1,∗ , Robin J. S TUART 2 , Vanessa ANDALO 3 , Ugur GOZEL 4 and Michael E. ROGERS 2 1 Entomology and Nematology Department, Institute of Food and Agricultural Science, University of Florida, Gainesville, FL 32611-0620, USA 2 Citrus Research and Education Center, Institute of Food and Agricultural Science, University of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850, USA 3 Entomology Department, University of Lavras, Lavras, MG, 37200-000, Brazil 4 Canakkale Onsekiz Mart University, Faculty of Agriculture, Department of Plant Protection, 17100 Canakkale, Turkey Received: 8 December 2006; revised: 28 February 2007 Accepted for publication: 1 March 2007 Summary – Steinernema texanum n. sp. is characterised by morphometrics of the infective juvenile with body length = 756 μm, distance from anterior end to the excretory pore = 59 μm, tail = 73 μm, ratio a = 25, H% = 59 and E% = 81. The lateral field pattern of the new species is 2, 7, 2, and is typical for the species. The male of the first generation can be recognised by the spicule and the gubernaculum lengths and shapes, position of the excretory pore, D% = 67 and GS% = 75. The female can be recognised by the vulva with very low epiptygma and two wart-like structures anterior to the tail tip that are always present on the ventral side. Steinernema texanum n. sp. is characterised genetically by the sequence of the ITS region (sequence length = 956 bp, the length of ITS1 = 263 bp, ITS2 = 286 bp, composition of its sequence and by 18 autapomorphies) and by sequence of D2D3 regions (sequence length = 860 bp, its composition and 15 autapomorphies). Steinernema texanum n. sp. is closely related to species in the feltiae-group, which include S. akhursti, S. feltiae, S. hebeiense, S. jollieti, S. kraussei, S. kushidai, S. litorale, S. monticolum, S. oregonense, S. sangi, S. silvaticum and S. weiseri. Isolates of the new species were obtained using the Galleria-baiting technique from soil samples taken near Kingsville, Texas, USA. Keywords – D2D3, description, entomopathogenic nematodes, molecular, morphology, morphometrics, phylogeny, SEM, taxonomy. Entomopathogenic nematodes have been known since 1923 but interest in the use of nematodes as biolog- ical control agents waned until the 1970s and 1980s. During that period, increasing environmental concerns about the use of chemical pesticides and their reduced availability reawakened interest in entomopathogenic ne- matodes for insect control. In 2001, about 100 differ- ent laboratories were exploring these nematodes and their bacterial symbionts in more than 60 countries from every inhabited continent (Gaugler, 2002). Many sur- veys have been conducted all over the world in search of species to control economically important insect pests (Hominick, 2002). Currently, 56 species of entomopatho- genic nematodes in the family Steinernematidae and 12 species in Heterorhabditidae have been reported (Nguyen, 2006). ∗ Corresponding author, e-mail: kbn@ufl.edu Laboratory experiments, and field releases of ento- mopathogenic nematodes in the past, show that they have been used successfully to control insect pests (Klein, 1990; Shapiro-Ilan et al., 2002). The isolation of S. scap- terisci Nguyen & Smart, 1990 from Uruguay and S. rio- brave Cabanillas, Poinar & Raulston, 1994 from Texas are good examples of successful searches for, and subsequent use of, entomopathogenic nematodes for biological con- trol (Parkman et al., 1993, 1994; Parkman & Smart, 1996; Shapiro-Ilan et al., 2002). These two nematodes are com- mercialised and sold for controlling mole crickets and cit- rus root weevils, respectively, in the USA. Steinernema riobrave has proved to be one of the most effective entomopathogenic nematodes yet tested for inundative biological control of root weevils such as Diaprepes abbreviatus (L.) in Florida citrus groves (Shapiro & McCoy, 2000a, b; Shapiro-Ilan et al., 2002). However, until recently, only a single strain of this species was known. Therefore, in an effort to find new strains © Koninklijke Brill NV, Leiden, 2007 379 Also available online - www.brill.nl/nemy