Gracilacus epacris




Rev 09/12/2023

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Morphology and Anatomy Life Cycle

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           Gracilacus epacris (Allen and Jensen, 1950), Raski, 1962

Type species of the genus

      Paratylenchus epacris

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Morphology and Anatomy:


Female:  Small, 0.31 mm, vermiform and become obese with time.

Stylet long (111 µm),  flexible.


Juvenile: Stylet present, esophagus well developed.

Male: Common, esophagus degenerate.

[Ref: Raski, 1962)

Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:

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Central and northern California.

Described from California black walnut, Juglans hindsii, from Tulare County, California.

Also, Yolo, Sonoma and Alameda counties, California.

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Economic Importance:

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Young, vermiform, female inserts its long stylet into root tissues and remains attached to the root surface by the stylet. Nematode feeds in epidermal, cortical parenchyma and sclerenchyma cells. Feeding induces cell wall thickening.

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California black walnut (Juglans hindsii), oak (Quercus sp.) and California laurel (Umbellularia californica).

For an extensive host range list for this species, click


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Life Cycle:

Ecophysiological Parameters:

For Ecophysiological Parameters for this species, click If species level data are not available, click for genus level parameters


Young, vermiform, female inserts its long stylet into root tissues and remains attached to the root surface by the stylet. Female body swells as gonads mature. Eggs are deposited in a gelatinous matrix which surrounds the female, eggs and and newly hatched J2s.

Fourth stage juvenile females (J4f) are inactive and lack a stylet; they do not feed.  They retain the cuticle of the previous stage.  Esophagus well developed.

Fourth stage juvenile males (J4m) are inactive, lack a stylet, have degenerate esophagus.

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Host Plant Resistance, Non-hosts and Crop Rotation alternatives:

For plants reported to have some level of resistance to this species, click
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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. Nematology 8:97-115.

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Copyright © 1999 by Howard Ferris.
Revised: September 12, 2023.