Steinernema kraussei

(Steiner, 1923) Travassos, 1927

DESCRIPTION

Males: Head truncate, slightly offset from the rest of body. Fused lips bearing two circles of papillae, inner-labial with six papillae and outer-cephalic with four papillae. Pore-like amphid opening located laterally in the cephalic papillae circle. Cuticle smooth with slight annulation visible under SEM. Tail portion curved ventrally when fixed; rounded tip bears a fine mucron. Eleven or 12 pairs of genital papillae present, one single papilla just in front of cloacal opening. Of these, 5 to 6 pairs preanal situated subventrally in two fine rows, 3 pairs adanal in lateral to dorso-lateral position, and 3 pairs postanal at the tail tip. Mouth opening triangular, stoma wall represented by sclerotized cheilorhabdions and beneath this by another and smaller prorhabdions. Esophagus muscular with a characteristic rhabditoid cylindrical corpus, subdivided into procorpus and slightly enlarged metacorpus. Isthmus narrow and distinct. Basal bulb enlarged with a valve. Excretory pore always anterior to nerve ring situated in the metacorpal portion. Testis monorchic, reflexed. Spicule shape variable but a well curved spicule is more common. Spicule head variable in shape (FIG.SEM) somewhat longer than wide. Shaft mostly present, sometimes indistinct. Rostrum often present. Two internal ridges present. Blade mostly well curved as in FIG.SEM A,D but less curved blades (FIG.SEM B,C,E) also observed. Velum present, extending about two- third blade length. Spicule tip with an aperture ventrally and a bluntly rounded or flattened terminus. In lateral view, the gubernaculum tapering anteriorly to a ventrally curved end. In ventral view, cuneus short, Y-shaped, pointed posteriorly, not reaching the end of corpus.. Second generation males are smaller than first generation males.

Measurements: First generation male : (n = 10) L = 1400 micrometers (um) (1200-1600); greatest width = 128 um (110-144); esophagus length = 152 um (139-178); distance of excretory pore from anterior end = 81 um (73-99); spicule length = 49 um (60-65)[straight line from head to tip]; gubernaculum = 33 um (29-37); tail length = 39 um (36-44), D%=53; SW=1.1; GS=0.68.
 

 Females: Head rounded, not offset from the rest of body. Cuticle slightly annulated. The arrangement of lips, papillae, alimentary tract similar to those of males. Excretory pore opening more anteriorly than in males. Tail pointed in young females of the first generation, with a postanal swelling, but blunt with a short spine in mature females, rarely without a spine. Slightly or moderately elevated vulva situated closely behind midbody. Gonads paired, reflexed. Second generation females are smaller, tail always pointed, rarely with postanal swelling.

 Infective juveniles: Body thin, 797 to 1102 micrometers long J2 cuticle sometimes present as a sheath. Head with four cephalic papillae, labial papillae indistinct. Oral opening closed, esophagus collapsed, basal bulb more elongated than in adults. Excretory pore opening near mid-esophagus (aproximately 46% esophagus from anterior end). Lateral fields with eight ridges (Fig. 2D). The central pair less distinct and the two ridges merge occasionally along the length of lat field. Tail pointed without any constriction or spike-like structure.

 Measurements: Length=951 micrometers (um) (797-1102), Width=33 um (30-36), anterior end to excretory pore=63 um (56-66), to nerve ring=105 um (99-111), esophagus length=134 um (119-145), Tail=79 um (69-86), width at anus=20 um (19-22), a=29, b=7.1, c=12.1, D=0.47, E=0.80.

Diagnosis : Excretory pore of adults is situated far in front of the nerve ring, close to mid-esophagus while in S. glaseri it is close to the nerve ring. Male tail with fine mucron which is absent in S. glaseri. Spicule tip is pointed without hook-like structure which is present in S. Glaseri. Length to width of manubrium is 1 to 1 while in S. glaseri it is 1.5 to 1. Rostrum usually developed while never present in S. glaseri. Infective juveniles of S. kraussei belong to the group of species characterized by medium body length, averaging below 1000 micrometers (um) and they are much thinner (33 um in width) than S. glaseri , 45 um ( P o i n a r 1978). Lateral fields with 8 ridges in both species, but the central pair is less prominent in S. kraussei.

REFERENCE

Mracek, Z. 1994.  Steinernema kraussei (Steiner, 1923) (Nematoda: Rhahditida: Steinernematidae): redescription of its topotype from Westphalia. Folia parasitologica 41:59-64.

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