Rev 12/17/2024
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Gracilacus Raski, 1962
Type species of the genus: Gracilacus epacris (Alien & Jensen, 1950) Raski, 1962
Synonyms: None.
The name is derived from the Latin gracilis (slender) and acus (pin).
The genus Gracilacus Raski, 1962 was distinguished from Paratylenchus by the following characters:
Gracilacus is distinguished from the genus Cacopaurus Thorne, 1943 by:
(Raski, 1976)
Raski (1962) 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; Siddiqi, 2000). 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., 2016).
Authorities remain split on the validity of Gracilacus. Some retain it as a valid genus (e.g. Andrassy, 2007) while others liist the species formerly assigned to this taxon as Paratylenchus (e.g. Nguyen et al., 2004, Ghaderi et al., 2014) (Ghaderi et al., 2016).,
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Labial framework weakly sclerotized.
Stylet long (41 to 199 um - approximately 1.5 to 3 times that of Paratylenchus) and flexible.
Excretory pore from level of base of stylet to level of nerve ring.
Annuli smooth, more rarely (three species) with small tubercles.
Females monovarial.
Stylet generally present, well developed.
Male: When males are present they lack a stylet or the stylet is much reduced.
Monorchic
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, 1962)
Lateral field 4 lines
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Lateral field 3 lines, stylet 54-88 um
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Female stylet <69 um, no vulva flap
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Female stylet 61-69 um, tail slender
G. acicula
Spermatheca present
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Stylet average length 77 um (70-85 um), females slender
G. mira
Female stylet 48-71 um
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Lips rounded
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Tail short, blunt, males common
G. epacris
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 ring
G. marylandica
D-rated pest in California Nematode Pest Rating System.
First described by Allen and Jensen from black walnut in Tulare County, California..
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).
Andrassy, I. 2007. Free-living Nematodes O Hungary. Vol 2. Hungarian Natural Histroy Museum.
Brown G.L. 1959. Three new species of the genus Paratylenchus from Canada (Nematoda: Criconematidae). Proc. Helminth Soc. Wahington 26:1-8. Esmaeili, M., Ramin Heydari, Pablo Castillo, Mozhgan Ziaie Bidhendiand Juan E. Palomares-Rius. 2015. Molecular characterisation of two known species of Paratylenchus Micoletzky, 1922 from Iran with notes on the validity of Paratylenchus audriellus Brown, 1959. Nematology 18:591-624. .
Geraert, E. (1965). The genus Paratylenchus. Nematologica 11, 301-334.
Ghaderi, R., Kashi, L., Karegar, A. 2014. Contribution to the study of the genus Paratylenchus Micoletzky, 1922 sensu lato (Nematoda, Tylenvnchuldae) Zootaxa 3841:151-187.
Ghaderi, R., Geraert, E., Karegar, A. 2016. TheTylenchulidae of the World. Academia Press, Ghent, Belgium
Raski, D.J. and Luc, M. 1987. A reapraisal of Tylenchina (Nemata) 10. The superfamily Criconematidea Taylor, 1936., Rev. Nematol. 10: 409-444..
Raski, D.J. 1976. Revision of the Genus Paratylenchus Micoletzky, 1922 and Descriptions of New Species. Part III of Three parts--Gracilacus. J. Nematology 8:97-115.
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.
H. Ferris.
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.
Siddiqi. M.R. (2000). Tylenchida parasites of plants and insects, 2nd edition.Wallingford, UK, CABI Publishing.
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