Nematology , 2001, Vol. 3(6), 503-514 Steinernema loci sp. n. and Steinernema thanhi sp. n. (Rhabditida: Steinernematidae) from Vietnam Ke Long P HAN 1 , Ngoc Chau NGUYEN 1 and Maurice MOENS 2;¤ 1 Institute of Ecology and Biological Resources, National Centre for Science and Technology, Nghiado,Caugiay,Hanoi, Vietnam 2 CLO-Department for Crop Protection, Burg. Van Gansberghelaan96, 9820, Merelbeke and Gent University, Laboratory for Agrozoology,Coupure 555, 9000 Gent, Belgium Received: 5 December 2000; revised: 1 May 2001 Accepted for publication:5 May 2001 Summary – Two new species of Steinernema (Rhabditida), Steinernema loci sp. n. and S. thanhi sp. n., were isolated from beach soil in Thanhhoa and Hatinh provinces in the northern part of Vietnam. A combination of morphological, morphometric and rDNA-RFLP features indicated the distinctness of both species from other Steinernema spp. Diagnostic characters of Steinernema loci sp. n. include: total body length (896-1072 ¹m), distance from anterior end to excretory pore (EP D 71-86 ¹m), tail length (66-83 ¹m), lateral eld in mid-body with eight ridges (nine distinct lines) and rounded, broad and smooth anterior end of the third stage infective juvenile; rst generation males were characterised by body width, spicule length and the ratio spicule length : anal body width (SW). Diagnostic characters of Steinernema thanhi sp. n. third stage infective juveniles include: total body length (720-960 ¹m), EP (68-84 ¹m), tail length (52-72 ¹m), lateral eld in mid-body with eight ridges (nine distinct lines) and rounded, broad and smooth anterior end. Spicule length, ratio SW and arrangement of genital papillae characterised the rst generation males. Keywords – entomopathogenic nematodes, RFLPs, Steinernema arenarium , S. feltiae , S. glaseri , S. karii, S. kraussei , S. longicaudum , S. neocurtillae , S. oregonense . In tropical and sub-tropical regions, the entomopatho- genic nematode genera Steinernema and Heterorhabdi- tis (Rhabditida) have received increased attention in re- cent years. Several new species have recently been de- scribed from these areas including: S. karii (Waturu et al., 1997) from Kenya, S. abbasi (Elawad et al. , 1997) from Oman, S. monticolum (Stock et al., 1997)from Korea, and S. siamkayai (Stock et al. , 1998) from Thailand. In Vietnam, S. tami was detected from primary forest in Cat Tien National Park along the Dong Nai river, Viet- nam (Luc et al., 2000). A survey conducted in Vietnam by Nguyen et al. (1999) yielded several steinernematid pop- ulations. Morphological observations and rDNA-RFLP analysis indicated that three new species were present. The rst species was detected in Xuanmy, Thuongxuan (Thanhhoa province) and described as Steinernema sangi (Phan et al., 2001). Two other species which were found in Thachkhe,Thachha (Hatinh province)and Haithanh, Tin- hgia (Thanhhoa province) in the northern part of Vietnam are described below. ¤ Corresponding author, e-mail: m.moens@clo.fgov.be Materials and methods SAMPLING Soil samples (ca 500 cm 3 ) were collected to a depth of 20 cm. Entomopathogenicnematodeswere extractedfrom soil by the Galleria baiting method (Bedding & Akhurst, 1975). Infective juveniles were collected from Galleria cadavers using the method of White (1927) and stored at 15 ± C in foam. MORPHOLOGICAL OBSERVATIONS For light microscopy,specimens were reared on G. mel- lonella. Infective juveniles were collected for 1 week af- ter their rst emergence from the insect cadavers, and adults of the rst generation were dissected from the ca- davers (Nguyen & Smart, 1995). These nematodes were killed and xed in hot formalin 4% (50-60 ± C), and kept in this solution for 48 h. Fixed nematodes were transferred to anhydrous glycerine according to Seinhorst’s (1959) c ° Koninklijke Brill NV, Leiden, 2001 503