Steinernema monticolum

Stock, Choo & Kaya, 1997

DESCRIPTION

Males:  General shape of body and anterior region similar to other species. Excretory pore opening  located at posterior 1/3 of metacorpus, just anterior to nerve ring. Testis single, reflexed. Tail conoid with mucron.  21-23 genital papillae as usual. Six pairs are subventral preanal (pair 6 may be adanal), 1 pair lateral preanal, 1 pair lateral postanal, 2 pairs ventral postanal and 1 pair subterminal or absent sometimes. Spicules brown-orange; paired and curved. Spicule head rounded . Calomus present. Lamina with 2 internal ribs. Velum present and extending from base of manubrium to proximal 2/3 of lamina. Gubernaculum arcuate, large, from 1/2 to 2/3 length of  spicules. Anterior end of gubernaculum curved ventrally and its posterior end forked. Cuneus long. Corpus wide, large and bifurcate posteriorly. Second generation males similar to first generation ones but smaller.

 Measurements (n = 20): Length=1600 um (1360-1840), greatest width=160 um (117-206), stoma length=4 (3-5), stoma width=6 (5-7), distance from anterior end to excretory pore=94 (75-113), to nerve ring=116 um(94-128), width at the level of excretory pore=49 um (45-52), esophagus length=166 um (152-184), testis reflexion=370 um (334-398), tail length=38 (31-41), mucron length=10 um (8-12), width at cloaca=49 um (38-67), spicule length=70 um (61-80), spicule width=8 um (7-10), gubernaculum length=45 um (35-54), gubernaculum width=3 um (2.5-5.0), SW (spicule length divided by width at cloaca)=1.4 (1.2-1.5), GS (gubernaculum length divided by spicule length)=0.6 (0.5-0.7), EW (distance from anterior end excretory pore divided by width at excretory pore)=1.9 (1.6-2.2), D (distance from anterior end to excretory pore divided by distance from anterior end to oesophagus base)=0.55 (0.49-0.61).

 Females: General morphology similar to males except posterior region and reproductive system. Ovaries amphidelphic, reflexed in dorsal position; oviduct well developed, glandular spermatheca and uterus in ventral position. Vagina short, with muscular walls. Vulval lips not protruded. Vulval opening near mid-body. Tail short, blunt, with mucron. Second generation females similar to first generation ones but smaller and tail longer.

 Infective juveniles. Body slender, tapering to both ends. Cuticle with transverse striae. Lip region smooth, mouth closed. Oesophagus degenerate. Nerve ring located at level of isthmus. Excretory pore  in anterior 1/3 of esophagus. Basal bulb valvate. Cardia present. Anterior portion of intestine with dorsally displaced pouch containing symbiotic bacterium. Lumen of intestine narrow, rectum long; anus distinct. Genital primordium evident. Tail conoid with pointed terminus.

 Measurements: Length=706 micrometers (um)(612-821), greatest width=37 um (32-46), distance from anterior end to excretory pore=58 um (54-62), to nerve ring=88 um (81-93), oesophagus length=124 um (120-131), tail length=77 um (71-95), width at anus=18 um (14-23), a=19 (14-22), b=5.7 (5.0-6.4), c=9.3 (7.6-11.1), D%=47 (44-50), E%=76 (63-86).

Type host. Unknown in nature, from bait-insect (G. mellonella) in sandy silt soil under larch (Larix leptolepis, Pinaceae).

 Type locality. Mount Jiri, Sancheong, Gyeongnam province, Korea.

Type specimens:
Holotype. Male first generation, University of California Davis Nematode Collection (UCDNC), Number UCDNC-3312, field collection number Jiri I-11.
Allotype. Female first generation, University of California Davis Nematode Collection (UCDNC), Number UCDNC-3313.
Paratypes. Males first generation, UCDNC-3314, females first generation, UCDNC-3315 and third stage infective juveniles, UCDNC-3316.

Etymology. The species is named for the geographic location from which it was isolated.

Diagnosis

Steinernema monticolum can be distinguished in all stages from other members of the genus by the location of the excretory pore, which is at the level of posterior 1/3 of metacorpus. The tail of the males of the first and second generation has a large mucron. In the males, ratio D is 0.55 (0.49-0.61). Other diagnostic characters are the shape of the spicules and gubernaculum, and the arrangement of the genital papillae, and the tail length. In the infective juveniles, the average body length is 706 um, the average body width is 37 um (32-46), and ratio a is 19 (14-22).

Life cycle of Steinernema monticolum is similar to other Steinernema species.
 

Symbiotic bacterium

 Like other Xenorhabdus species, the Phase I of this bacterium was characterized by the adsorption of neutral red and bromothymol blue from McConkey agar and NBTA, respectively. Further studies on this Xenorhabdus sp. will be conducted to provide a more specific identification.

REFERENCE

StocK, S. P. , H. Y. Choo and H. K. Kaya 1997. An entomopathogenic nematode, Steinernema monticolum sp. n. (Rhabditida: Steinernematidae) from Korea with a key to other species.
Nematologica 43:15-29.

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