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Gracilacus Raski, 1962
The name is derived from the Latin gracilis (slender) and acus
The genus Gracilacus Raski, 1962 was distinguished from
Paratylenchus by the following characters:
Gracilacus is distinguished from the genus
Cacopaurus Thorne, 1943 by:
established the genus Gracilacus essentially
to differentiate those Paratylenchus species
with a stylet longer than 48 μm. Several nematologists have considered Gracilacus as
a valid genus, others have
not agreed and have synonymized Gracilacus with Paratylenchus (Geraert, 1965;
Recent studies on the ITS rRNA gene showed that phylogenetic relationships
of putative species included in Gracilacus are
not resolved, and the validity of this genus is in question (Esmaeli et al.,
Labial framework weakly sclerotized.
Stylet long (41 to 199 um - approximately 1.5 to 3 times that of Paratylenchus)
from level of base of stylet to level of nerve ring.
smooth, more rarely (three species) with small tubercles.
Stylet generally present, well developed.
Male: When males are present they lack a stylet or the
stylet is much reduced.
Caudal alae absent or comprised of thickened evaginations of cuticle.
[Ref: Raski (1962), Raski & Luc (1987), and H. Ferris.]
Key to species of Gracilacus (slightly modified from from Raski,
Lateral field 4 lines
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Lateral field 3 lines, stylet
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Female stylet <69 um, no vulva flap
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Female stylet 61-69 um, tail slender
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length 77 um (70-85 um), females slender
Female stylet 48-71 um
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Tail short, blunt, males common
Female ave length 0.39 mm, male without
stylet or male unknown
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Tail conocal with rounded tip
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Female stylet average
length 67 um (63-71 um), male unknown
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Female ave. length 0.39 mm (0.34-0.42 mm), excretory pore near nerve
in California Nematode Pest Rating System.
First described by Allen and Jensen from black walnut in Tulare County,
Based on stylet length, probably feeding on deeper cell layers than Paratylenchus.
Walnut, grape, oak, laurel.
Fourth stage juveniles survive for long periods; 42 months in plastic bags,
80 days in saturated soil. Cuticle of J4 less permeable than in adults (Kondo
and Ishibashi, 1979).
genus Paratylenchus. Nematologica
Kondo, E and N. Ishibashi. 1979. Ultrastructural changes associated with
development of pin nematode, Gracilacus sp., with special reference to
its survival. Appl. Ent. Zool. 14:1-11.
Raski & Luc, Rev. Nematol. 10(4):409-444 (1987)
Raski, D.J. 1962. Paratylenchidae n.fam. with description of five new
species of Gracilacus n.g. and an emendation of Cacopaurus Thorne, 1943,
Paratylenchus Micoletzky, 1922 and Criconematidae Thorne, 1943. Proc.
Helminthol. Soc. Washington 29:189-207.
Raski, D.J. 1976. Revision of the Genus Paratylenchus Micoletzky, 1922
and Descriptions of New Species. Part III of Three parts--Gracilacus. J.
parasites of plants and insects, 2nd edition.Wallingford,
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