Steinernema ceratophorum

Jian, Reid & Hunt, 1997

DESCRIPTION

    Females: Body spiral or C-shaped when heatkilled. Cuticle with fine transverse striae  under SEM. Lateral field and phasmids inconspicuous. Head truncated to slightly round, continuous with body; mouth opening circular. Six labial and 4 cephalic papillae arranged as in other species. Stoma partially collapsed: pharyngeal collar absent; esophagus extending near to mouth opening. Cheilorhabdions located beneath lips and composed of thick, cuticularized ring, appearing as two dark dots under a compound microscope . Below this is another cuticularised ring, presumably prorhabdions; meso-, meta- and telo-rhabidions are vestigial and presumably occur in collapsed area of stoma. Esophagus typical of family; procorpus cylindrical and muscular; metacorpus slightly swollen, non-valvate; isthmus distinct; basal bulb muscular, with small, distinct valve. Nerve-ring surrounding isthmus. Esophago-intestinal valve almost bilaterally symetrical and projecting into intestine. Excretory pore opening usually anterior to nerve-ring; somewhat variable in location. First generation females larger (average length: 5.37 mm) than second generation females (average length: 1.7 mm). Vulva a transverse slit; vulval lips usually protruding slightly from body surface. Vagina short, leading into amphidelphic genital tracts. Females lay eggs initially, but later eggs hatch inside female body with juveniles boring their way out. First generation female tail shorter than anal body width,  with small mucronate projection on tip. In contrast, posterior region of second generation female tapering evenly posteriorly, and ending  with a fine mucron about 5.5 micrometers long.

    Male: Similar to females but smaller and with male reproductive system. Body curved posteriorly,  when heat-killed. First generation male ( 1.38 mm long) larger than second generation male ( 0.9 mm long). Gonad monorchic, reflexed. Spicules paired, symmetrical, curved, with distinct dark yellow coloration; spicule head elongate; head length about 1.5 times or more than head width, somewhat angular in shape; small rostrum  present; velum extending nearly to tip of lamina. Each spicule has 2 internal ribs. Gubernaculum boat-shaped in lateral view and distally forked in ventral or dorsal view; anterior part thin with or without a proximal hook, ventrally curved, cuneus simple in dorsal view. Bursa absent.There are 23 genital papillae (11 pairs plus one single) arranged as: 6 precloacal. subventral pairs, most posterior being near cloaca; one single ventral papilla located  just anterior to cloaca; one adcloacal subdorsal pair located near the proximal section of gubernaculum; 2 postcloacal subventral pairs and 2 subdorsal pairs near tail tip. Tail short, rounded conoid and lacking mucron in both first and second generations.

     Measurements (Male, first generation, n=35): L=1358 SE=134 (1136-1694) um, W=146 SE=21 (104=185)um, stoma length=12 SE=1 (9-15), stoma width=7 SE=1 (5-8) um, EP=85 SE=11 (50-104)um, width at excretory pore=56 SE=6 (45-72)um, NR=123 SE=14 (90-147) um, ES=165 SE=10 (149-190) um, testis reflexion=393 SE=94 (163-574) um, anal body width=52 SE=5 (45-70) um, tail length=30 SE=4 (23-38) um, spicule length=71 SE-7 (54-90) um, spicule width at head=11 (9-16) um, at neck=9 (7-11) um, at lamina=11 (7-14) um, gubernaculum length=40 SE=4 (25-45) um, gubernaculum width=7 SE=1 (5-9) um, D%=51.4 SE=7.2 (32.8-64.8) EW=1.5 SE=0.3 (07-2.0), SW=1.4 SE=0.2 (1.0-2.0), GS=0.6 SE=0.1 (0.4-0.8), c'=0.6 SE=0.1 (0.4-0.8).

    Infective stage juveniles: Infective juveniles often enclosed in the 2nd stage cuticle. Body slender, gradually tapering from base of espophagus to anterior end and from anus to terminus. Cuticle with fine transverse striae; lateral field  with 6 or 8 longitudinal ridges in mid-body region as seen under light microscope and with SEM. Marginal and submarginal ridges are less distinct than other ridges, and space (groove) between  ridges are not even. Lip region continuous, rounded and hemispherical with pair of lateral horn-like structures near the oral opening ; mouth and anus closed; esophagus and intestine collapsed. Excretory pore located in anterior region of esophagus (D% = 45.6). Anterior portion of intestine with pouch containing cells of symbiotic bacteria. Tail straight, conoid, tapering evenly to a pointed terminus; terminal spine absent. Hyaline region about half tail length.

    Measurements(n=45): L=706 SE=62 (591-800) micrometers (um), W=27 SE=3 (23-34) um, head to excretory pore=55 SE=5 (47-70) um, width at excretory pore=19 SE-1 (16-23), head to nerve ring=92 SE=6 (79-103) um, esophagus length=123 SE=7 (108-144), anal body width=15 SE=2 (9-18), tail length=66 SE=5 (56-74), a=25.9 SE=1.1 (23.7-27.9), c=10.6 SE=0.9 (8.8-12.9), D%= 45 SE=3.1 (40.0=55.8), E%=84.2 SE=6 (73.8-96.4), c'=4.2 SE=0.4 (3.3-5.1).

DIAGNOSIS AND RELATIONSHIPS

Steinernema ceratophorum  is characterised by the following combination of characters: infective stage juvenile with a body length of about 706 (591-800) um; juvenile lip region with a double horn-like structure and lateral field with six or eight longitudinal ridges; tail tip of both first and second generation males lacking a cuticular mucron; spicules curved with a distinct dark yellow coloration, about 71 and 54 um long in first and second generation respectively; first generation female tail conoid with a small mucronate projection; and second generation female tail tapering evenly posterior to salient posterior anal lip and ending in a fine mucronate process about 5.5 um long. The RFLP banding pattern is also unique when compared to a library of 33 other Steinernema spp. The new species is morphologically similar to S. affine, S. intermedium, S. riobrave and S. bicornutum, but can be separated from these four species by a combination of morphological, DNA and cross-breeding techniques. Only one other species is recorded as having two horn-like structures on the infective juvenile head, viz. S. bicornutum.  In addition, S. ceratophorum can be further distinguished by the following characters: the spicule length of both first and second generation males is longer than S. bicornutum (71 vs 65 um; 54 vs 51 um) whereas the gubernaculum is shorter (40 vs 48 um; 31 vs 33 um) and second generation male tail lacks a small mucron, recorded as present in S. bicornutum; from S. affine in lacking a mucron on the male tail tip; from S. intermedium by the first generation male having a shorter spicule (71 vs 91 um) which is dark-yellow rather than grey or colourless, a smaller average length of gubernaculum. (40 vs 62 um), and in lacking a ventral concavity in the tail (Poinar, 1988); from S. riobrave by the first generation male spicules being longer (71 vs 67 um), the shorter gubernaculum (40 vs 51 um), the GS ratio (length of gubernaculum divided by spicule length) being lower (0.6 vs 0.7) (Cabanillas et al., 1994) and the negative cross-breeding test.

Etymology: Derived from the Greek keratos = a horn and phoreus = a bearer (horn-bearer).

REFERENCE

JIAN, H., A. P. REID & D. J. HUNT, 1997. Steinernema ceratophorum n. sp. (Nematoda: Steinernematidae) a new entomopathogenic from north east China. Systematic Parasitology 37:115-125.

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