Females, second generation : Similar to first generation female but smaller and slender body. Tail straight, longer than width at anus, tapering or pointed, bearing a mucron.
Males, first generation : Anterior region similar to first generation females but much smaller. Testis single, reflexed. Spicules paired with internal ribs. Velum thin. Spicule head variable in shape, usually broad, slightly angular. Neck short. Lamina moderately curved with blunt tip. Gubernaculum boat-shaped in lateral view, and ventrally curved, with a knob anteriorly. Twenty-three genital papillae, variable in position. Six pairs preanal, one pair in the region of gubernaculum, and four pairs postanal. A single genital papilla just anterior to cloaca. Cloacal opening slit-like. Tail conoid, ventral portion usually concave, tip blunt without mucron. Bursa absent.
Measurements (n=20): Length=1680 micrometers (um) (1560-1820), width=138 um (104-161), stoma length=3.9 um (3-4), stoma width=5.9 um (5-6), anterior end to excretory pore=112 um (95-139), to nerve ring=111 um (101-133), esophagus length=154 um (139-182), testis reflexion=197 um (99-392), tail=29 um (24-32), width at anus=47 um (38-55), spicule length=71 um (65 73), spicule width=11.7 um (9.9-11.9), gubernaculum length=56 um (52-59), gubernaculum width=8.2 um (5.9-9.9), D%=73 (64-75).
Males, second generation: Similar to first generation male but smaller, slender body and tail usually bearing a mucron.
Infective juveniles: Often enclosed in the cuticle of the second-stage. Body slender, tapering to both end. Lateral fields distinct with six to eight ridges. Lip region smooth, generally continuous. Mouth and anus closed. Esophagus long and narrow, basal bulb weak. Intestine collapsed. Nerve ring distinct. Hemizonid located at level of basal bulb. Anterior portion of intestine with a pouch containing symbiotic bacteria. Tail conical with pointed terminus.
Measurements: Length=980 um (820-1110), width=34 um (28-38), anterior end to excretory pore=66 um (60-72), esophagus length=132 um (116-138), tail=70 um (64-78), a=30 (24-37, b=7.6 (6-8), c=14 (12-16)
Type host and locality : Nematodes were recovered by using Galleria mellonella (L.) larvae as bait from a soil sample collected in a grass field near Grants Pass, Oregon, USA. The natural host is unknown.
Type specimens: Holotype (male, first generation) and allotype (female, first generation) deposited in the Nematode Collection at the University of California, Davis, California. Paratypes deposited in the United States Department of Agriculture Nematode Collection, Beltsville, Maryland.
Diagnosis and reiationship
The average length (977 um), ratio D (0.5) and ratio E (1.0) in infective juveniles, the absence (in first gencration) and the presence (in second generation) of a tail mucron and moderately curved spicules in males separate S. oregonense from all other previously described species of Steinernema. The length ranges of infective juveniles of S. oregonensis are different from those of S. rarum, S. ritteri, S. carpocapsae, S. scapterisci, S. kushidai, S. riobrave, S. intennedium, and S. cubanum. The length range of S. oregonense infective juveniles somewhat overlaps with those of S. affine, S. arenarium, S. feltiae, S. glaseri, S. neocurtillae, and S. puertoricense. However, the ratio E (anterior end to the excretory pore/tail length) of the infective juveniles of S. oregonense does not overlap with those of S. feltiae, S. neocurtillae and S. glaseri. The ratio D (anterior end to the excretory pore/anterior end to the pharynx base) separates S. oregonense from S. puertoticense. Males of S. oregonense can be separated from those of other Steinernema species by the absence (in first generation) and the presence of a tail mucron and moderately curved spicules. The absence of a tail mucron in first generation males separates S. oregonense from both S. affine and S. feltiae. The moderately curved spicules separates S. oregonense from S. intermedium and S. riobrave, in which the spicules are usually strongly curved (a line running parallel with the calomus and lamina forms an angle of 70-90 degrees). S. oregonense is closely related to S. arenarium, S. cubanum, and S. glaseri in general morphological characters. The blunt tip spicules separate S. oregonense from notched tip spicules of S. glaseri and swollen tip spicules of S. arenarium. The presence of a tail mucron in second generation males separates S. oregonense from S. cubanum. The males of S. oregonense have a ventral concave tail. which is different from S. arenarium and S. glaseri. S. oregonense is reproductively isolated from S. arenarium, S. fieltiae and S. glaseri as indicated by negative results in the cross-breeding tests.
Life cycle: S. oregonense has a life cycle comparable to that of other described species of Steinernema. At room temperature (ca 22 degree C), it takes 3-4 days for infective juveniles to reach the adult stage of the first-generation, and another 2 days to reach the second-generation adults. It usual1y takes one week for the nematode to complete its cycle, and emerge from insect cadavers as infective juveniles.
REFERENCE
Liu, J. and R. E. Berry 1996.
Steinernema oregonensis n.sp. (Rhabditida: Steinernematidae)
from Oregon, USA. Fundamental and Applied Nematology
19:375-380.
This document was constructed and is maintained by KHUONG
B. NGUYEN
Entomology & Nematology Department
University of Florida