Steinernema sasonense

Steinernema sasonense

Phan, Spiridonov, Subbotin & Moens, 2006

Des= cription

= Male

Body fusiform, C-shaped in heat-relaxed specimens, tapering towards anterior end. Cuticle annulation 1.2-1.5 μ= ;m wide, poorly distinguishable throughout the body. Lateral fields absent. Anterior extremity rounded with flattened area just around oral aperture. S= ix labial and four prominent, 2-3 &= #956;m high, cephalic papillae. Cheilostom cuticle connected to thick, strongly cuticularized, 2.5 μm long ring of 6-6.3 μm dia= m., forming middle part of stoma. Additional thinner cuticular ring situated posterior to thicker one, embedded in pharynx tissue. Corpus 16 μm diam., cylindrical, wi= thout visible swelling around stoma, metacorpal swelling up to 18-19 μm width. Basal bulb subspherical. Nerve ring situated on anterior slope of basal bulb in most specimens. Valves in form of platelets= of thin folded cuticle. Cardia with vacuoles, protruding for 8 μm into intestine. Excret= ory channel strongly cuticularized for 10 μm from pore. Intestinal lumen broad for 150-200 μm from bulb, then with na= rrow meandering lumen up to 130-160 &= #956;m long posterior to ventricle. Separate spermatocytes quickly disappearing in flexed testis region. Vas deferens walls vacuolated. Genital papillae with a row of usually nine pairs of subventral papillae extending from tail terminus to mid-body, one large, unpaired, precloacal papilla (not so protruding in this species as other ones described here) in midventral position, one pair of papillae in lateral position at manubrium level when spicules retracted, and one pair of papillae in dorso-lateral position in postcloacal area. Spicules (Fig.1) with elongate, funnel-shaped manubrium, tapering towards distal end, with r= ound extremity and more or less pronounced terminal duct. No bifurcation of outer line of velum and ventral rib of spicule observed near rostrum. All four ma= in ribs of spicule discernible, but ventral-most rib tightly adpressed to inner one. Spicule blade gradually narrowing from rostrum to distal end. Cloacal opening covered by flap when spicules retracted. Two papilla-like structure= s on edges of cloacal opening. Distal half of velum edge strongly cuticularized. Gubernaculum usually straight with slightly curved proximal end. Tail mucron present, in form of short, rounded spike, 2 μm long.

Some measurements: Spicule length = =3D 71 (66-78) μm, gubernaculumn l= ength =3D 53 (50-56) μm, D% =3D 40 (37-45), SW % =3D 250 (219-306), GS% =3D = 75 (69-82).

= Female

Cuticle annulation poorly discernible. Cephalic extremity with six labial and four cephalic papillae. Cuticular ring forming main part of stoma walls 5-6 μm thick and 7-7.5 μm long. Stomatal cavity = 12 μm width. Excretory duct strongly cuticularized, entering body at angle of about 45&= deg;. Vulva equatorial with petal-like, 12-14 μm long structures protruding from opening. Vulval lips less th= an 10 μm high, equal in= size. Tail terminus dome-shaped, bearing 12-14 μm long, spike-like mucron.

Infective juvenile

Body of heat-relaxed juveniles moderately C-shaped, tapering towards anterior en= d. Cephalic extremity hemispherical with four protruding cephalic papillae. Li= ning of buccal cavity forming protruding plug with triradiate lumen. Annules abo= ut 1 μm wide, visible througho= ut body. Lateral field in anterior body half with four ridges in centre, two pronounced marginal ridges and poorly discernible submarginal lines. Such regular pattern not observed in posterior half of body with ventral gap bet= ween central and marginal ridges disappearing. Lateral field lines disappearing = at level of phasmids. Lateral field 8-9 μm wide at mid-body. Corpus slender, slightly widening to metac= orpus. Nerve ring located slightly posterior to corpus-isthmus junction. Hemizonid= on isthmus level. Basal bulb with valves poorly visible. Cardia about 10 μm long, cylindrical, sli= ghtly narrowing to posterior end. Bacterial vesic1e round or nearly round, 5-8 μm long, loosely filled w= ith 2-4 μm long, rod-lik= e, bacterial cells. Rectum about two anal body width long. Genital primordium = 60 μm long. Phasmids located= at 25% of tail length posterior to anus (phasmid-mucron distance about 35-36 μm, with aperture near ve= ntral edge of ventral marginal line. Tail with or without slightly pronounced ven= tral concavity, conical, with some irregularities in shape, terminus sharply pointed. Hyaline region comprising less than half of tail length.

Some measurements: L =3D 486 (456-5= 16) μm, EP =3D 32 (30-34) μm, T = =3D 47 (42-52) μm, D% =3D 32 (30-34), E% =3D 69 (61-76).

Typ= e host and locality

Natural host unkn= own as species was obtained by the Galleria mellonella baiting method from = the southern slope of the Chumomray mountain near Sason, Sathay in Kontum provi= nce, Vietnam (longitude 107"43', latitude 14°27', altitude 700 m a.s.l.= ). Soils were humid, fernalie acrisols of primary broad-leaved forest growing = on the slopes of granite mountains.

Type material

Holotype male and= six paratype males deposited at Institute of Parasitology of Russian Academy of Sciences, Leninskii prospect 33, Moscow, 119071, Russia. Slides with paratype males, first generation females and infective juveniles deposited in Department of Nematology, Institute= of Ecology and Biological Resour= ces, National Center for Science and Technology, Hoang Quoc Viet 18, Nghiado, Caugiay, Hanoi, Vietnam.

Rel= ationships

Males have two papilla-like structures on the margin of the cloacal aperture, the spicules have an elongate manubrium and a well developed rostrum, and there is a sho= rt, rounded, spike-like mucron present on the tail terminus. The first generation females have a pronounced conical tail mucron and long, p<= /span>etal= -like, epiptygmata. The body length of the infective juvenile is, on average, shor= ter than 500 μm, the lateral field h= as four ridges in the mid-body region and the hyaline region comprises less th= an 50% of the tail length.

This species can be distinguished from S= . scapterisci by the IJ length (437-502 vs 517-609 μm), and fro= m S. cumgarense and S. eapokense by H% (38-48 vs 48-59, 47-57, respectively. The pharynx is shorter in S. sas= onense than in S. carpocapsae <= /i>(94-104 vs 103-190 μm) and D% =3D 28-33 vs 23-28 in S. carpocapsae.=

Mol= ecular characterisation

Steinernema sa= sonense is characterised by sequence lengths of ITS regions (ITS1 + 5.= 8S + ITS2) 742 bp, ITS1 =3D 278 bp, ITS2 =3D 307 bp and its composition, A =3D 0= .22642, C =3D 0.16576, G =3D 0.21832, T =3D 0.38948. The sequence of ITS regions is d= eposited in GenBank under accession no. AY487919.

Dis= tribution

In addition to the type locality, this species was also isolated from primar= y, closed, broad-leaved forest mixed with some conifers. This habitat was situ= ated on the slope of a sandstone and gneiss mountain in Thachnham (Mangla) near Konplong, Kontum province (longitude 108°25', latitude 14°38', alti= tude 1210 m a.s.l.). Soils were humid, fernalie acrisols (Phan et al., 2006). =

Reference

Phan, K.L., Spiridonov, S.E., Subbotin, S.A. = & Moens, M. (2006). Four new species of Steinernema Travassos, 1928 with short infective juveniles from Vietnam. Russian Journal of Nematology 14, 11-29.