Steinernema bicornutum

Tallosi, Peters & Ehlers, 1995

DESCRIPTION

    Males: Males have a single reflexed testis. Sperms have a diameter of 4-5 um. Anterior to the cloacal opening a row of 6 pairs of genital papillae in ventro-lateral position and a single ventral precloacal papilla. Three pairs posterior to the gubernaculum and another 3 pairs surrounding the tail tip. Spicules paired and light brown in color. In first generation males, two different types of spicules occur. Type I spicules (FIG.SEM) are curved; capitulum distinct and well separated from lamina, proximally broad and flattened; calamus with a small pointed protrusion. From this point a distinct velum extends almost to the proximal end of the lamina. Spicule tip with a transverse incision, similar to the spicule of S. carpocapsae. Type II spicules (10-20 % of the population) are much less curved; lamina extending to capitulum without distinct demarcation; velum absent or indistinct; spicule tip without incision; color usually a little darker; proximal hook of gubernaculum usually more pronounced than in type I males. Spicule morphology similar to S. feltiae. Tails of first generation males of both types are short and round and without a mucron. Second generation males have a longer tail usually with a small mucron. The gubernaculum is spindle-like. Only one type of spicule is present similar to type II of the first generation.

     Measurements: Length=1352 micrometers (um), width=109 um (80-128), anterior end to excretory pore=82 um (68-98), to nerve ring=123 um (108-137), esophagus length=156 um (138-168), tail=32 um (25-35), spicule=65 um (53-70), gubernaculum=48 um (38-50), D%=50.

     Females: Cuticle smooth, head rounded, not offset from rest of the body. Each of the 6 lips bearing a single labial papilla. Outer circle of 4 cephalic papillae further back on the head. Stoma short and wide. Esophagus muscular and almost cylindrical, but widening towards the basal end. Metacorpus nonvalvated; isthmus much thinner than metacorpus; nerve ring surrounding esophagus between isthmus and basal bulb. Valve ridges of basal bulb indistinct; basal bulb slightly broader or as wide as metacorpus. Excretory pore situated slightly anterior to isthmus, almost at the middle of the esophagus. First generation females often produce giant forms >1 cm. Gonads amphidelphic with opposed reflexed ovaries. Vulva a transverse slit protruding only in second generation, and never in first generation females. Protruding of vulva lips less pronounced than in other steinernematids. Tail of first generation short, blunt, with a short wedge-shaped projection and always with mucron. Tail of second generation longer and always with mucron.

    Infective juveniles: Head hemispherical, labial region bearing a hornlike structure composed of two protuberances, which possibly are laterally protruding labial papillae, located on an oval ring around the oral opening. The horn-like structure is exclusively found in the infective juvenile and in lateral view, the two horns might be misidentified as the similar but single tooth observed on heterorhabditid infective juveniles. The third stage infective juvenile is generally ensheathed by the second stage juvenile cuticle. Observation of the horn-like structure is occasionally prevented by the presence of the second stage cuticle. Amphidial openings lateral, a little further back from the lip region, almost covered by the two horns. Four distinct cephalic papillae arranged medially on the head at a 45 degrees angle to the hornlike structure. Excretory pore situated half-way between head and bulbus. Esophagus and intestine lumen collapsed. In the anterior portion of the intestine, a pouch is present containing cells of the symbiotic bacterium, probably Xenorhahdus sp. Body slender with transverse annulations. Lateral field with 8 ridges of which the submarginal ridges are less distinct than the others. Tail constricted with a pointed end.

     Measurements: Length=770 micrometers (um), width=30 um (25-33), anterior end to excretory pore=61 um (53-65), to nerve ring=92 um (88-100), esophagus length=124 um (113-135), tail=72 um (63-78), hyaline part of tail=33 um (28-38), a=27 (23-29), b=6.2 (5.6-6.9), c=10.7 (9.7-12.0)D%=50 (40-60), E%=80 (80-100).

     Type locality: Strazilovo, Vojvodina, south of Novi Sad, Yugoslavia, in the Furska Gora Mountains. No type host can be named as the species was isolated using wax moth larvae as bait.

     Type material: Holotype and paratypes deposited in the German Nematode Collection at Biologische Bundesanstalt, Institute for Nematology and Vertebrate Research, Miinster, Germany. The strain designation of the type population is YuS-Wo 6.

     Differential diagnosis: Steinernema bicornutum sp. n. can be readily distinguished from all other described Steinernema spp.by the presence of a double horn-like papillae on the lip region of infective juveniles.

   REFERENCE

Tallosi, B. and R. Ehlers 1995. Steinernema bicornutum sp. n. (Rhabditida: Steinernematidae) from Vojvodina, Yugoslavia. Russian Journal of Nematology 3:71-80.

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