Dolichodorus heterocephalus Cobb,
The genus Dolichodorus was erected by Cobb ( 1914) when he
named D. heterocephalus from fresh water at Silver Springs, Florida and
Douglas Lake, Michigan.
Length, female: 2.1-2.7 mm; length, male: 1.7-2.2 mm.
Head somewhat flattened dorso-ventrally,
with four prominent lobes (2 subdorsal, 2 subventral) which have a
continuous outline in face view and are not separated from each other
by deep clefts as in, for example, Belonolaimus
longicaudatus. In lateral view, head rounded, set off
from body by deep constriction and with nine or more faint transverse
lines corresponding to the eight or more minute head annules.
When specimens are not quite lateral, the head appears wider due to
its dorso-ventral flattening.
Long stylet with cone longer than shaft. Stylet flexible, bends with body. Has strong
backward sloping knobs 6.5-7.5 µm across.
Esophageal lumen folded in procorpus
when stylet retracted.
Basal esophageal bulb elongate-pyriform, butting with
intestine, with 3 nuclei,
one larger dorsal nucleus situated about half-way along bulb, and 2
smaller subventral nuclei at the same level or posterior to
pore variable in position, 75-130 annules
behind head; at its most forward position opposite the anterior half
of the median bulb,
but more generally opposite the posterior half of the bulb to the
level of the nerve ring.
usually 4 annules long, 14-44 (28 av.) annules behind excretory pore.
Vulva a transverse slit with a pair of opposing
sclerotized pieces in lateral view.
Ovaries paired, outstretched, spermathecae
Intestine extending beyond rectum to form a sac.
Anterior part of tail rounded or
the conoid spike of the posterior part. Paracer et al. (1968)
noted that females of D. heterocephalus with bluntly
rounded tails appeared occasionally in a Massachusetts
field with 3 incisures, completely
the middle line first appears a few annules behind the head, the outer
lines arising some annules further back. Posteriorly, the outer
lines disappear, leaving the central incisure on the tail.
Phasmid inconspicuous situated on the central line
posterior to anus.
[Ref: CIH Descriptions of Plant-parasitic Nematodes,
Set 4, No. 56 (1974)]
Similar to female, except for
slightly arcuate, distal end of gubernaculum
with small reflexed process, tip protruding from body.
Males have unique caudal alae,
well-developed, finely crenate, and trilobed; tail terminus with small
notch, seen in dorsal or ventral view.
Smart et al. (1973) describe the presence
of an outer uterine layer or protein coat on the egg, thought to be
the first report of such a layer on the egg of a plant-parasitic
Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:
Eastern U.S., especially Florida (wet areas); also in virgin soil in South
Africa. In Zimbabwe, I encountered Dolichodorus on roots of a Julbernardia
tree at 7 ft. below soil surface near water
table, although the species was not confirmed).
Cranberry bogs in Massachussetts.
Related genus Neodolichodorus occurs in wet areas of
Napa Valley and
Coastal range of California, for example a citrus tree near a well in Yountville, on a bay
tree next to a stream near Lake Berryessa.
in California Nematode Pest Rating System.
Ectoparasite mainly at root tip; nematode has long stylet.
During feeding of D. heterocephalus, Paracer et al.
(1967) observed discrete root galls, curvature at the root tips and
localized lesions in the root cortex and epidermis. There was some
enlargement of nuclei in cortical cells at the feeding site.
The root damage leads to plant stunting and other effects of
Celery, sweet corn, water chestnut, bean, tomato, pepper, cranberry, cabbage,
balsam, and carnation.
Nematode prefers wet locations with high soil moisture.
Field infestations in Florida may be due to soil spreading from riverbanks
onto fields and into irrigation water (Christie,
Males and females are both present.
Life history parameters not well known. Paracer et al. (1968) gives some
information on the biology of Massachusetts populations: the first larval molt
occurs in the egg; second stage juveniles hatch after 14-17 days at 20-23
Males, females, and all larval stages feed, individuals sometimes remaining
at one location on the root for up to 7 days.
The nematode does not survive in fallowed pots for longer than 3
Several different biotypes of D. heterocephalus may be present
(Florida and Massachusetts populations) (Paracer et al., 1968); they are
distinguished by the host status of celery to them.
Feeding causes brownish cortical lesions and enlarged cortical nuclei; root
elongation ceases; secondary roots are attacked, resulting in stubby-root
symptoms; some terminal galling may be observed.
Perry (1953) observed severe stunting, accompanied by depleted root systems
of celery and corn, in field infestations of D. heterocephalus in
Florida. Celery yield was reduced by 50% in one field.
Water chestnut growing in hydroponic beds was also stunted; nematode feeding
also causes stunting of tomato, bean, and pepper (Perry, 1953).
Damage is reported on a range of plants, including celery, garden
balsam and sweet corn, in moist sandy soils (Christie, 1952; Tarjan et al.,
1952; Perry, 1953; Paracer et al., 1967).
Use of nematicides, such as 1,3-Dichloropropene
(Telone) or, earlier, ethylene dibromide (EDB).
Drying of moist soil areas gives effective control.
[Would dry fallow for at least
3 months also be effective under field conditions?]
Host Plant Resistance, Non-hosts and Crop Rotation alternatives:
Christie, J.R. 1952. Some new nematodes of
critical importance to Florida growers. Proceedings - Soil Science Society
of Florida 12:30-39.
CIH Descriptions of Plant-parasitic Nematodes, Set 4, No. 56 (1974)
Cobb, N.A. 1914. The North American free-living fresh-water nematodes.
Transactions of the American Microscopical Society, 33: 69-133.
Paracer, S.M. and B.M. Zuckerman. 1967. Monoxenic
culturing of Dolichodorus heterocephalus on corn root callus.
Paracer, S.M., M. Waseem and B.M. Zuckerman.
1967. The biology and pathogenicity of the awl nematode, Dolichodorus
heterocephalus. Nematologica 13:517-524.
Perry V.G. 1953. The awl nematode, Dolichodorus
heterocephalus, a devastating plant parasite. Proceedings of the
Helminthological Society of Washington 20:21-27.
Scheck, H. 2021, California Pest Rating Proposal
for Dolichodorus heterocephalus Cobb, 1914. CDFA website.
Tarjan, A.C., B.F. Lownsbery and W. D. Hawley.
1952. Pathogenicity of some plant-parasitic nematodes from Florida soils. I.
The effect of Dolichodorus heterocephalus Cobb on celery.