Nematode
of the Week
Gracilacus
latescens
Photo
Gallery
Gracilacus latescens Raski, 1976
Syn. Paratylenchus (Gracilacus) latescens
(Raski, 1976) Siddiqi, 1986
Tylenchulidae: Paratylenchinae
This week's featured nematode comes
to us from the Konza Prairie LTER
in Manhattan, Kansas, USA. The most notable features of this nematode
are its small size (260 - 288 mm in our specimens,
with an average of 270 mm) and its extremely
long stylet (64.8 - 71.2 mm, average 68.6 mm).
As part of a survey
of nematodes associated with various tallgrass prairie plants, we've found
G.
latescens associated with roots of several grasses, including big bluestem,
little bluestem, Scribner's panicum, and bluegrass. In this species, as
in at least some other species of Gracilacus, the mature females
are sessile endoparasites and as they feed, become large and swollen with
age. Since we have not yet dissected any roort tissue (focusing on
soil extracts), we have not recovered any such swollen forms from our samples.
Peter
Mullin
Description (from Raski,
D.J. 1976. Revision of the genus Paratylenchus Micoletzky,
1922 and descriptions of new
species. Part III of three parts - Gracilacus. J. Nematol.
8: 97-115):
Paratypes (19 slender females):
L
= 0.27 (0.22-0.29) mm; a = 19 (14-23); b = 2.2 (1.7-2.5);
c
= 13 (10-13); V =
16 (14-18) 71 (68-73); stylet = 75 (63-80) mm;
prorhabdion = 67 (58-740 mm; excretory pore
= 71 (64-82) mm.
Holotype (female): L
= 0.25 mm; a = 17; b = 2.3; c = 10; V = 17
72; stylet = 71 mm; prorhabdion = 63 mm;
excretory pore
= 74 mm.
Paratypes (8 males): L
= 0.29 (0.25-0.35) mm; a = 26 (20-29); b = 3.5 (3.3-3.7);
c
= 12 (11-13); spicules = 20 (18-23)
mm; gubernaculum = 4 mm; T = 37
(27-47); excretory pore = 65 (58-77) mm.
Allotype (male): L
= 0.35 mm; a = 29; b = 3.6; c = 13; spicules = 23
mm;
gubernaculum = 4 mm;
T = 47; excretory
pore =
77 mm.
Paratypes (5 swollen females):
L
= 0.37 (0.36-0.39) mm; a = 5.5 (4.1-9.3); b = 3.8 (3.6-4.1);
V
= 78-79 [see
drawing,
fig.
5-6]; excretory pore = 111 mm.
Female:
Body almost straight, only slightly curved ventrad after fixation.
Head rounded; submedian lobes or lips only slightly distinguished on anterior
surface. Head sclerotization light; stylet guiding apparatus appears
as two darker, almost straight lines near base of sclerotization.
Stylet slender; slightly curved ventrad; knobs moderately developed, backwardly
directed. Length of stylet shaft, plus knobs 8 mm
[7 (5-10) mm in paratypes]. Excretory
pore near base of stylet [seedrawing,
fig. 1]. Hemizonid small; immediately posterior to excretory
pore. Valve in metacorpus 9 micrometers long. Isthmus distinct,
slender, 11 mm long, 2 mm
wide. Esophago-intestinal valve small, lobate. Ovary outstretched;
spermatheca elongate, about twice as long as wide; filled with sperm [see
drawing, fig. 2]. Vulva lips rounded; protrude slightly,
lateral vulvar membranes lacking. Tail broadly conoid; tapers only
slightly to bluntly rounded terminus. Average width of body annules
ranges from 1.0-1.4 mm (1.0-1.6 in paratypes).
Lateral field with 3 incisures equally spaced; inner incisure lighter than
outer 2 [see
drawing, fig 3].
Swollen
female: Body variously swollen; greatly variable in size [see
drawing, fig. 5-6]; often reniform with distinctly projecting tail.
Head rounded. Stylet of fully swollen females invariably broken in
collection process. Metacorpus greatly enlarged, 20-28
mm
in width; swells gradually but major swelling 30-35 mm
long. Isthmus remains slender but posterior bulb enlarges slightly
to 9-10 mm wide by 11-13 mm
long. Ovary coils many times; few eggs seen are oval, nearly spherical
and occur singly in uterus. Body narrows abruptly immediately posterior
to vulva; then becomes broadly conoid; tapers slowly to blunt rounded terminus.
Cuticle very thick, with annules coarse, especially in head region.
Lateral field indistinct in most swollen females; seen as 3 incisures in
a few. Tail elongate and terminus bluntly rounded. Swollen
females found completely inside root tissues of host plant.
Male:
Body curves slightly ventrad after fixation. Head rounded; sclerotization
light [see
drawing, fig. 7]. Stylet lacking; esophagus degenerate.
Hemizonid immediately posterior to excretory pore. Testis outstretched,
with large, irregularly-shaped cells in anterior half; filled with numerous
smaller sperm in posterior half [see
drawing, fig. 8]. Testicular gland distinct (40-49 mm
in paratypes). Spicules curve very slightly ventrad. Cloacal
sheath short, without projecting posterior margin. Indistinct caudal
alae extend about 8-9 mm anterior and posterior
to cloacal opening. Tail broadly conoid; annules distinct almost
to bluntly rounded terminus. Average width of body annules ranges
from 1.0-1.4 mm. Lateral field with 3
incisures as in female.
This species is most closely related to G. aculenta from which it
differs in longer stylet [58 (51-66) mm for
G.
aculenta] and length of esophagus (b = 2.4-4.1 in G. aculenta).
Type
host: mesquite, Prosopis sp.
Type
locality: Weslaco, Texas.
Distribution:
9 females, 3 males and 2 juveniles found in soil about roots of Mesembryanthemum
sp. at Dillon Beach, Marin County, California; 7 females, 2 males and 3
juveniles from soil about strawberry, Noyo, Mendocino County, California.
Notes:
Determined by Peter Mullin. G. latescens is apparently rare
in prairie soils (we've only seen 7 slender females out of over 4000 nematodes
examined; no males or juveniles of sthis species have been observed); this
may be due in part to its endoparasitic feeding habit later in life.
We have also recovered one specimen of G. aculenta (i.d. based primarily
on stylet length and b ratio) from our Konza samples. In addition,
specimens of an undetermined Gracilacus species have been recovered
from 9 Mile Prairie near Lincoln, Nebraska, which are similar to G.
latescens, except that the slender females appear to uniformly retain
the fourth-stage juvenile cuticle and the stylet, while very degenerate,
remains visible in the males.
Comparison between G. latescens paratypes and
specimens from Konza Prairie:
Measurements:
|
Paratypes:
|
Konza Specimens:
|
L (mm):
|
270
|
270.4
|
b:
|
2.2
|
2.31
|
V:
|
71
|
72.0
|
Stylet (mm):
|
75
|
68.6
|
References:
Raski, D.J. 1976. Revision of the genus Paratylenchus Micoletzky,
1922 and descriptions of new species. Part III of
three parts - Gracilacus. J. Nematol. 8: 97-115.
Raski, D.J. 1991. Tylenchulidae in agricultural soils.
Chapter 17, pp. 761-794 in: Manual of Agricultural
Nematology, W.R. Nickle, ed. Marcel Dekker, Inc., New York.
Siddiqi, M.R. 1986. Tylenchida: Parasites of Plants and
Insects. Commonwealth Agricultural Bureaux, Slough, UK.
645 pp.
|