Steinernema khoisanae
Nguyen
, Malan & Gozel, 2006
Description
Male, first generation Fig. 1
Body slender, C-shaped to strongly curved posteriorly, when heat
killed. Head rounded, gently tapering
anteriorly, slightly swollen in some specimens. Face view with six labial papillae,
two amphids and four cephalic papillae. Stoma shallow and narrow, usually
with pronounced cheilorhabdions. Excretory pore posterior of nerve ring,
located mostly in the vicinity of, but sometimes posterior to basal bulb. Pharynx with cylindrical procorpus,
metacorpus slightly swollen, isthmus present.
Nerve ring in anterior part of isthmus, basal bulb distinct. Pharyngo-intestinal valve present. Lateral field present in midbody, with one
narrow ridge. Spicules paired, light
brown in color. Head (manubrium)
of spicules, somewhat elongate (1.28-1.56); shaft (calomus) very short or
absent; blade (lamina) thick, tapering slightly posteriorly; blade terminus
blunt; velum present. Each spicule with two internal ribs. Gubernaculum boat-shaped in lateral view, cuneus
arrowhead-shaped. Usually a single
precloacal papilla and eleven or twelve pairs (66%) of genital papillae
arranged in normal position for Steinernema (i.e., six or seven pairs
precloacal subventral, one pair adcloacal, one pair lateral, two pairs
subterminal and one pair subdorsal). In
one male (of 12 nematodes for SEM observation), one single papilla and fourteen
pairs were observed. The number of
caudal papillae is constant (3 pairs), but the number of precloacal subventral
pairs is variable. Tail conoid; tail
terminus without mucron.
Second-generation male similar to that of the first-generation male
except body length shorter and body diam. less.
Body C-shaped or strongly spiraled when heat killed and fixed with 4% formalin. Head rounded and continuous with body. Body cuticle smooth or with faint annules. Lateral fields with one line and present on all females observed. Phasmids inconspicuous. Cheilorhabdions prominent, well sclerotized. Another smaller sclerotized structure present, posterior to cheilorhabdions, presumably the prorhabdions. Pharynx with procorpus cylindrical, muscular; metacorpus swollen; isthmus distinct; basal bulb enlarged, valvate. Nerve ring surrounding isthmus, just anterior to basal bulb. Oesophago-intestinal valve prominent. Excretory pore position variable, from near mid-pharynx to mid-basal bulb. Pharyngo-intestinal valve present. Vulva a transverse slit not protruding from body surface, without an epiptygma. Tail digitate, with a postanal swelling in most females, more pronounced in fully mature females. Tail shorter than anal body width, tapering to a blunt end. Two projections present at tail end with dorsal projection more pronounced..
Body an open C when heat killed and fixed with 4% formalin. Similar to first-generation female but
smaller. Body diameter greater anterior
to vulva than posterior to vulva. Vulva
on asymmetrical protuberance and situated at midbody. Postanal swelling present.
Tail tapering gently to a sharp point.
Infective juvenile
Body elongate. Sheath
(second-stage cuticle) present immediately after harvesting, but many
infective juveniles losing sheath in storage. Exsheathed juvenile
with four cephalic papillae. Labial
region smooth, continuous with body.
Amphids prominent. Cuticle
marked with prominent transverse striations.
Excretory pore 0.5-1 body diameter anterior to nerve ring. Lateral field beginning anteriorly with one
line at the first annule. At annules 8-15, two additional lines appear forming
two ridges. Near excretory pore level, number of ridges in lateral
fields increasing from two to seven.
Near the end of pharynx, the central ridge dividing into two, making a
total of eight, the maximum number in the lateral field. Posterior to mid body, number of ridges in
lateral field becoming six. In
posterior third of body, two marginal ridges disappearing gradually, a short
distance anterior to anus, only four ridges remaining in lateral field. Near mid-tail, four ridges in lateral field
reducing to two ridges. With the above
arrangement, the formula of the lateral field is 2, 7, 8, 6, 4, 2. Pharynx with thin corpus, metacorpus slightly swollen, isthmus
present, nerve ring usually at middle of isthmus; basal bulb elongate with
visible valve. Cardia present. Bacterial pouch located just posterior to
cardia, 10.1 (9.3-10.5) μm in diameter, 15.2 (15-17) μm in length,
containing bacterial cells, variable in shape, mostly oval. Genital primordium prominent 156 (130-207)
μm in length. Hemizonion very
distinct, near mid basal bulb, about 130 (118-141) μm from anterior end
for isolate SF80, and 121 (113-130) μm for isolate SF87. Tail four times as long as anal body
diameter and attenuate. Phasmid present
or absent; when present, very small, near mid-tail. Hyaline portion occupying 58% (54-61) of tail length.
Diagnostic
characters
Steinernema khoisanae is characterised by morphometrics
of the infective juvenile with body length 1076 μm, narrow body diameter
33 μm, distance from anterior end to the excretory pore 94 μm, tail
85 μm, a ratio 33, D% = 68, H% = 57, and E% = 111 (bold faced numbers in. Lateral pattern of the species is 2,
7, 8, 6, 4, 2. Male of the first generation can be recognised
by the spicule and the gubernaculum shapes, position of the excretory pore near
the end of the pharynx, D% = 88, and SW ratio = 1.99. Female can be recognized by the vulva not protruded and tail with
prominent mucron.
Molecular
Steinernema khoisanae is characterised molecularly by sequence
lengths and compositions of ITS and D2D3 regions (Nguyen et al., 2006)
a- ITS region lengths, 1051 base pairs (bp), ITS1 =
314 bp, ITS2 = 330 bp and its composition
(A = 0.25309, C = 0.19886, G = 0.24263, T = 0.30542) (accession # DQ314287).
b- D2/D3 region length, 876 bp, its composition
A = 0.24138, C = 0.19397, G = 0.31466, T = 0.25000 (DQ314289).
More DNA information is available in Nguyen et al. (2006).
Relationships
Steinernema khoisanae is closely related to nematode species in the glaseri
group, which include S. apuliae Triggiani et al.,
2004, S. arenarium, S. cubanum, S. diaprepesi, S. glaseri,
S. guangdongense, S. longicaudum
and S. puertoricense.
The infective juvenile of S.
khoisanae differs from S. cubanum
in body length of 1283 (1149-1508) μm versus 1075 (904-1214) μm for S. khoisanae. It differs from S.
puertoricense in the body width of 51 (47-54) μm versus 33 (27-39) μm
for S. khoisanae From S.
glaseri, this species
differs in the position of the nerve ring and the length of the pharynx 120
(112-128) μm and 162 (158-168) μm, respectively, versus 108 (93-116) μm
and 138 (115-147) μm for S.
khoisanae. From S. arenarium, S. guangdongense, S.
diaprepesi and S. longicaudum, this species differs in the
position of the excretory pore, 83 (76-86) μm, 80 (71-83) μm, 74
(66-83) μm and 82 (76-89) μm, respectively, in these four species
versus 93 (84-100) μm in S. khoisanae.
The first-generation male of this species differs from all related
species by the position of excretory pore which is near the end of pharynx with
the D% = 80, higher than all related species, shape of spicule (Nguyen &
Smart, 1997, Fig. 2). Arrowhead-shape
of cuneus of S. khoisanae
differs from S. cubanum, S. glaseri, S. puertoricense,
S. diaprepesi, S. longicaudum (cuneus of these species are Y-shaped)
and S. arenarium (cuneus V-shaped).
The first generation female of S. khoisanae differs from S. puertoricense, S. diaprepesi and S. guangdongense
in the absence of an epiptygma. It also
differs from S. puertoricense, S. longicaudum
and S. apuliae in its absence of a
protruding vulva.
Vulva of S. khoisanae
is flat with the contour of the body or slightly shrunken. Lateral fields have one line in this species
while they are absent in S. aciari, S. diaprepesi, S.
guangdongense, S. glaseri and S. karii. Unfortunately, lateral fields of the female
of S. khoisanae cannot be compared with those of S. cubanum, S.
puertoricense and S. longicaudum, because lateral fields of these
species were not reported.
Type host and
locality
Steinernema khoisanae (SF80) was collected from a soil sample in the Cape Province,
South Africa, by means of laboratory trapping with G. mellonella. The nematode
was collected from bluegrass on a road side at latitude 33o12'.33S,
longitude 19º06'.57E. Natural host is
unknown.
Holotype (male, first generation):
Isolated from haemocoel of G. mellonella deposited in the
United States Department of Agriculture Nematode Collection (USDANC),
Beltsville, Maryland.
Nguyen, K.B. & Smart, Jr., G.C.
(1997). Scanning electron microscopic
studies of spicules and gubernacula for Steinernema
spp. (Nemata: Steinernematidae). Nematologica
43, 465-480.