Male (first generation): Body curved posteriorly. Cuticle with faint transverse striae. Lateral field and phasmids inconspicuous. Head truncate or slightly rounded . Lips fused,  six labial papillae and four sub medial cephalic papillae, amphids present. Stoma shallow, steinernematoid. Esophagus extending near to mouth opening. Cheilorhabdions beneath lips, forming a cuticularized ring. Below this another cuticularized ring, presumably prorhabdions; meso-, meta- and telorhab-dions are vestigial. Esophageal procorpus muscular and cylindrical; metacorpus slightly swollen; isthmus distinctly narrowing in both generation;  basal bulb muscular with small, distinct valve. Esophageal base set off from intestine. Cardia well developed. Excretory pore opening usually anterior to nerve ring at level of metacorpus. Nerve ring distinct, anterior to basal bulb. Gonad monorchic, reflexed. Spicules paired arcuate, symmetrical and distinct light golden yellow in coloration. Each spicule with two internal ribs of variable length; dorsal rib curved ventrally and extended to the posterior end; shaft short or absent; velum extending almost to proximal end of  lamina.  Spicule head elongate (FIG1) , broad not continuous with the blade. Blade (lamina) tapering to form a cylindrical part and then tapering again to sharply pointed distal tip. Gubernaculum boat-shaped in lateral view. In dorsal or ventral view anterior end of gubernaculum ventrally curved, enlarging gradually to form the corpus; bifurcated to form two wings. The length/greatest width is 3.6. Cuneus short, fine and needle-shaped and pointed posteriorly to form a Y- shaped structure. Bursa absent.
There are 23 genital papillae (eleven pairs and one single) distributed as in other Steinernema spp. Tail short, bluntly conoid,. Mucron present in 10% of males.
Measurements, in micrometers (n=20): L=1357 ± 89 (1163-1505), W=102 ± 10 (80-128), EP = 81 ± 4.8 (72-92), NR = 99 ± 6.3 (88-107), ES = 132 ± 5.8 (126-146), tail length = 25 ± 0.8 (24-27), ABW = 36 ± 2.3 (32-40), spicule length = 68 ± 3.6 (62-73), gubernaculum length = 41 ± 3.2 (36 -45), SW = 1.8 ± 0.1 (1.0-2.2), GS = 0.6 ± 0.04 (0.5-0.6), D%=60 ± 3 (50-60).

Male (second generation): Similar to first generation, differing by smaller size. Spicules and gubemaculums smaller than first generation. Tail short, dorsally convex, lacking a mucron.

Female (first generation): Heat killed specimens usually spiral or C-shaped. Cuticle with faint transverse striae. Lateral field and phasmids inconspicuous. Head truncate to slightly rounded continuous with body. Lips fused, bearing  six labial papillae and  four sub-medial cephalic papillae; amphids present. Stoma shallow. Anterior part of esophagus covering stoma. Cheilorhabdions  located beneath lips, composed of thick, cuticularized ring. Below this another cuticularized ring, presumably prorhabdions; meso-, meta-and telorhabdions are vestigial. Procorpus muscular, cylindrical; metacorpus slightly swollen, non-valvate; isthmus slightly narrow; basal bulb with small, distinct, valve. Basal bulb set off from intestine,. Cardia well developed. Excretory pore opening usually anterior to nerve ring at level of metacorpus. Nerve ring distinct, anterior to basal bulb. Gonads amphidelphic; reflexed ovaries. Vulva median in position, a transverse slit, vulval lips usually protruding slightly from body surface with weakly developed, double flapped, epiptygma (FIG2) . Vagina short, leading into the paired genital tracts. Tail short, not constricted, dorsally convex with bluntly rounded terminus, lacking mucron. Tail shorter than anal body width.
Female (second generation): Similar in general aspects to first generation female except smaller. Vulva a transverse slit, generally protruding from the body surface. Tail pro-portionally longer, conoid, longer than anal body with, ending in a fine mucron.
Infective stage juvenile: Body tapering smoothly at both ends. Cuticle with fine transverse striations. New  third stage juvenile is often
ensheathed in 2nd stage juvenile cuticle. Heat relaxed specimens straight to slightly ventrally arcuate. Lateral field distinct at midbody region with eight distinct lines (seven ridges). Phasmid inconspicuous. Head hemispherical, labial region bearing two horn-like structures  (FIG1) . Lip region bearing four distinct cephalic papillae, consisting of two subdorsal and two subventral, arranged medially on head. Cephalic region not set off. Mouth and anal openings closed. Excretory pore at mid-esophagus, with a long cuticularized excretory duct. Nerve ring distinct, located anterior to basal bulb. Esophagus long and narrow, distinctly narrower at level of nerve ring, terminating in a valvate basal bulb displaced dorsally. Cardia present. A bacterial pouch enclosed by intestinal wall located posterior to cardia. Lumen of intestine narrow. Rectum long and narrow, anus distinct. Tail conoid, tapering to a fine pointed terminus. Hyaline portion occupying about half the total tail length.
Measurements, in micrometers (n=20):L=683±21(649-716), W=27±1.2(24-29), EP=54±2.2(49-58), NR=80±2.1(76-83), ES=113±4.2(108-122),tail length=58±2.1(53-62), a=24±1.5(21-27), b=6±0.3(5-6), c=11±0.5(10-12), D%=47±2.7(42-53), E%=91±5(87-102)

Type host and locality: Soil around the roots of vegetables, in the Malir area, Karachi, Sindh. Also from grass and ornamental plants, Sonmiani beach and Mubarak village, Balochistan, Pakistan.
Type specimens: Holotype male (first generation) and numerous paratypes (males, females, first and second generations and infective stage juveniles) deposited in the nematode collection at the National Nematological Research Centre, University of Karachi, Karachi - 7527Q, Pakistan. Ten first generation males, ten second generation males, three first generation and five second generation females, ten infective stage juveniles deposited in the type collection at Entomology and Nematology Department, IACR- Rothamsted, Harpenden, Herts., AL5 2JQ, UK. Numerous paratype males and females (first and second generation) and infective stage juveniles on slides and pure live culture deposited in the nematode collection at CABI Bioscience, Bakeham Lane, Egham, Surrey TW20 9TY, UK.

Diagnosis and relationships:Steinernema pakistanense  can be separated from all species of the genus by having two prominent horn-like structures on labial region of third stage infective juveniles, a combination of morphological characteristics and unique RFLP profile with ITS region of the rDNA repeat unit. This new species comes close to species having two horns-like structures on the head of IJ, S. bicornutum, Tallosi, Peters & Ehler, 1995 and S. ceratophorum, Jian, Reid & Hunt, 1997. It can be differentiated from the most closely related species S. bicornutum by the following characteristics: smaller average body length of the infective stage juveniles 683 (649-716) um vs 769 (648-873) um, shorter tail length 58 (53-62) um vs 72 (62-77) um, males of first generation of S. pakistanense having only one type of spicule vs two different types of spicules (type I & type lI) in first generation males of S. bicornutum. Spicule tip without transverse incision.

Reference

Shahina, F. M. Anis, A. P. Reid, J. Rowe, and Maqbool. 2001.  Steinernema pakistanense sp. n. (Rhabditida: Steinernematidae) from Pakistan.
International Journal of Nematology 11:124-133.