Steinernema karii

Waturu, Hunt & Reid, 1997

DESCRIPTION

First generation females: Body obese, usually C-shaped on heat relaxation. Head truncate to rounded . Cuticle smooth, lateral lines not observed. Lip region with six fused lips, labial tips separate with a minute papilla on top. Outer circle with four cephalic papillae and and two lateral amphids. Stoma as described for other Steinernema species, tapering into oesophagus and lightly cuticularized. Esophagus more or less cylindrical with a slightly swollen basal bulb. Isthmus short and indistinct. Cardia well developed. Excretory pore and distal region of duct  uticularized, located approximately halfway along  oesophagus. Nerve ring at about two thirds or more of the oesophagus length from anterior end. In fixed specimens, excretory pore can be observed more  anteriorly. Intestine voluminous filled with numerous fat globules. Rectum short.  Vulva median   and slightly raised with small, double epiptygma. Vagina short, muscular. Gonads amphididelphic, reflexed. Oocytes in multiple rows,  uteri containing many eggs. Tail  short, initially dorsally convex-conoid with a ventral digitate-like peg and then becoming short and broadly rounded with a blunt terminus.

Second generation females: Similar to the first generation female, but smaller in size (1.6-2.6 mm), more slender and with fewer eggs in uterus.   Vulval region in younger females raised, epiptygma  less obvious. Tail longer than anal body width, conoid and more tapering to a digitate terminus.  The posterior anal lip is markedly raised.

First generation males: Body smaller than first generation females . Heat killed specimens J- shaped. Cuticle with  faint transverse striae. Lateral fields present, 3-4 um wide with  three ridges. Head rounded with six lips fused at base, each lip bearing a papilla. Four cephalic papillae distinct. Mouth  round with prominent lateral amphids. Stoma small. Oesophagus with a slightly swollen metacorpus, an indistinct isthmus and a rounded basal bulb. Cardia well developed. Excretory pore located at about two thirds of oesophagus length. Nerve ring crossing isthmus at slightly more than two thirds of the oesophagus length. Testis single and reflexed. Spicules paired,  strongly curved and light golden brown in color.  Spicule head about twice as long as wide, subangular and offset from the lamina. Lamina with ridges running to the spicule tip. Velum thin Gubernaculum arcuate in lateral view and distally bifurcate in ventral view, anterior end slightly recurved and hook-like. Cuneus present. Twenty three genital papillae present arranged as follows: six subventral precloacal pairs, a single precloacal midventral papilla; one sublateral precloacal pair; one subventral adcloacal pair; two subventral postcloacal pairs and a subdorsal postcloacal pair. Tail short, dorsally convex conoid, with a bluntly rounded terminus; mucron absent. Phasmid indistinct.

Measurements

 Holotype (Male, first generation): L=1.97 mm; body width=134 um; distance from anterior end to excretory pore = 125 um; total oesophagus = 169 um; width at excretory pore=74 um; anal body width=59 um; tail length=45 um; spicule (curved median line) = 80 um; gubernaculurn = 53 um; a=14.7; b=11.7; c=43.8; c'=0.8.

 Paratype( n=20): L=1900 SD=300 (1400-2400) um, W=136 SD=17 (107-166), EP=108 SD=14 (86-138) um, ES=164 SD=7 (146-187) um, anal body width=55 SD=5 (43-66), tail length=37 SD=7.5 (22-48) um, spicule length=83 SD=4 (73-91) um, gubernaculum length=57 SD=6 (42-64) um, D%=66 (53-78), SW=1.5, GS=0.7.

Second generation males: Similar to the first generation in many respects, but slightly smaller.

Third stage infective juveniles:  Body straight to slightly ventrally curved when relaxed.  Body smoothly tapering towards the anterior and posterior extremities; initially enclosed in 2nd stage juvenile cuticle which is usually lost with age. Cephalic region smoothly rounded and not set off from the body contour. Cuticle with transverse striae approximately 2.1 um wide at midbody. Lateral fields at midbody  with  seven ridges, the submarginal ridges being narrower than the others. Lip region bearing four distinct cephalic papillae and prominent lateral amphids. Oesophagus degenerate. Basal bulb usually displaced towards the dorsal contour. Hemizonid distinct, located at about anterior margin of  basal bulb. Excretory pore cuticularized, situated
at about mid-oesophagus.  Excretory duct long, cuticularized. Intestine separated from oesophagus by a cardia,  gut lumen containing numerous fat globules. Bacterial pouch well developed, located in anterior part of intestine. Tail conoid, tapering to a finely pointed terminus lacking a terminal cuticular spine. Hyaline portion occupying about half total tail length. Phasmids distinct, mid-tail in position but not in hyaline region.

Measurements (n=28): L=932 SD=24 (876-982) um, W=33 SD=1.4 (31-35) um, EP=74 SD=3 (68-80) um, NR=105 SD=5 (97-112) um, ES=134 SD=6.8 (122-147) um, anal body width=22 SD=0.6 (21-23) um, tail length=74 SD=4.5 (64-80) um, a=28.5, b=6.8, c=12.6, D%=56.6, E%=0.96.

TYPE HOST AND LOCALITY:

The natural host is unknown as larvae of the greater wax moth, Galleria mellonella, were used as a trap insect . The type locality is a field with a clay loam soil with acid-hurnic top planted to bananas and carrots at Kibingo, Kirinyaga district Central Province, Kenya. It is situated in the Upper midland agroecological zone at an altitude of 1400-1600 m. The species is widespread throughout central Kenya.
Type specimens: Holotype male (first generation) and numerous paratypes (males, second generation, female, first and second generation and infective juveniles) deposited in the nematode collection at the International Institute of Parasitology, St. Albans, United Kingdom. I'luee first generation males, five second generation males, three first generation females, five second generation females and ten U3 deposited in the type collections at each of Mus6um national d'Histoire naturelle, Paris, France and University of California, Davis, USA.

DIFFERENTIAL DIAGNOSIS

Steinernema karii is characterized by a combination of morphological characters and unique RFLP profiles within the ITS region of the rDNA repeat unit. The characters include: IJ length of 904 SD37 (832-974) um; distance from anterior end to excretory pore in IJ3 of 76 SD 6 (66-82) um; IJ tail length of 76 SD 6 (66-88) um; IJ lateral field with seven ridges; absence of a terminal spine on IJ tail; male first generation spicule length of 83 SD 4 (73-91) um; lack of a mucron on tail tip of males; spicule shape. This nematode is morphologically similar to S. arenarium  (=S. anomalae), S. neocurtillae Nguyen & Smart, 1992, S. caudatum , S. cubanum, S. felliae and S. glaseri. S. karii can be distinguished from S. feltiae in longer IJ body length (904 vs. 849 um), in lacking a mucron on the male tail and in  more posterior position of the IJ excretory pore (76 vs. 62 um); from S. neocurtillae in the much more posterior position of the IJ excretory pore (76 vs. 18 um) and the absence of a mucron on the male tail; from S. cubanum in shorter IJ body length (904 vs . 1283 um), longer IJ tail (76 vs. 67 gm), more anterior position of the IJ excretory pore (76 vs. 106 um); from S. glaseri in shorter IJ body length (904 vs. 1130 um), more anterior position of the IJ excretory pore (76 vs. 102 um) and lacking notched spicule tips; from S. caudatum in smaller IJ (904 vs. 1106 um) and slightly shorter tail (76 vs. 82 um); from S. arenarium in smaller mean length of IJ (904 vs. 1034 or 1217 um), more anterior IJ excretory pore (76 vs. 83 um) and spicule lacking a swollen tip.
 

Etymology: Named after the Kenya Agricultural research Instirute (KARI).

REFERENCE

 Waturu, C. N., D. J. Hunt & A. P. Reid, 1997. Steinernema karii Sp n. (Nematoda: Steinernematidae), a new entomopathogenic nematode from Kenya. International Journal of Nematology 7:68-75.

This document was constructed and is maintained by KHUONG B. NGUYEN
Entomology & Nematology Department
University of Florida