Comparative Parasitology 67(1) 2000 - Peru State College

Comp. Parasitol.
67(1), 2000 pp. 107-108
Research Note
New Host and Distribution Record of Gordius difficilis
(Nematomorpha: Gordioidea) from a Vivid Metallic Ground Beetle,
Chlaenius prasinus (Coleoptera: Carabidae) from
Western Nebraska, U.S.A.
BEN HANELT' AND JOHN JANOVY, JR.
School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0118, U.S.A.
(e-mail: bhanelt@unlserve.unl.edu; jjanovy@unlserve.unl.edu)
ABSTRACT: Gordius difficilis (Montgomery, 1898)
Smith, 1994 is recorded from a creek in a juniper forest
in western Nebraska. Subsequent pitfall data shows
Chlaenius prasinus Dejean, 1826 to be the definitive
host. This represents the first report of G. difficilis from
the American Midwest, of C. prasinus as a host of
nematomorphs, and as a host for G. difficilis.
KEY WORDS: Gordius difficilis, Chlaenius prasinus,
vivid metallic ground beetles, Nematomorpha, Nebraska,
U.S.A.
Nematomorphs are a well-recognized, widely
distributed but poorly studied phylum (Chandler,
1985). Sometimes referred to as horsehair or
gordian worms, freshwater nematomorphs are
obligate parasites as larvae but free-living as
adults.
Gordius aquaticus difficilis Montgomery,
1898 was originally described from a single
male specimen. Although Montgomery (1898)
recognized 5 structural differences between G.
aquaticus difficilis and Gordius aquaticus robustus
Montgomery, 1898, he assigned G. aquaticus
difficilis as a subspecies rather than a distinct
species. Based on this early description,
Miralles (1975) synonymized G. aquaticus difficilis
with G. robustus Leidy, 1851, but Chandler
(1985) synonymized G. aquaticus difficilis
with Gordius paraensis Camerano, 1892.
More recently, Smith (1994) used scanning
electron microscopy to show that G. aquaticus
difficilis is distinct enough to warrant considering
it as a separate species, G. difficilis. This
determination was based on the presence of a
parabolic line of hairlike structures anterior to
the cloacal opening, as well as the presence of
distinct areoles in the midbody of the female.
In mid-June 1998, G. difficilis was found in
1 Corresponding author.
107
White Gate Creek, Keith County, Nebraska
(41°12'20.5"N, 101°39'86.3"W). This site consists
of a first-order, spring-fed creek suirounded
by juniper trees (Juniperus scopulorum Sargent,
1897) and various deciduous vegetation. The
creek has a sandy bottom and often contains algal
blooms because of the use of the creek by
cattle. Nineteen free-living individuals were collected
from the creek between late June and late
July, 10 males ranging in size from 68-307 mm
and 9 females ranging in size from 89-208 mm.
Individuals were often found entangled in the
algae or attached to sticks or rocks on the banks
of the creek.
In late June 1998, 4 lines of 10 pitfall traps
were set adjacent to White Gate Creek. Of 6
trapped Chlaenius prasinus Dejean, 1826, 2
were infected with 3 worms each. None of the
other invertebrates trapped contained nematomorphs.
One host contained 2 female worms and
1 male worm; the other host contained 3 female
worms. The males ranged in size from 103-297
mm, and the females ranged in size from 185-
203 mm. The hosts were void of gonads, fatbodies,
and intestines but appeared to behave
normally.
Worms were killed in 70% EtOH and brought
up to 100% glycerine prior to examination. All
specimens were temporarily mounted in glycerine
for observation. Worms were as described
by Montgomery (1898) and Smith (1994). Briefly,
the male posterior is bifurcated with a subterminal
ventral cloacal opening (Fig. 1). A line
of hairlike structures curves around the anterior
end of the cloacal opening. Posterior to the cloaca
is a postcloacal crescent, extending about
one-fourth the length of the lobed ends. Females
have entire posteriors. Cuticular areoles are
more prominent in females compared with males
when viewed with light microscopy.
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