Page 1 Page 2 邸ic蠅迦c魍iC。エ工is (C。ーe。pteraz Euiichadidae

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Eulichas incisicolils (coleoptera: Eulichadidae), an important
decomposer of leaf litter in Asian tropical stream communities
HAYASHI, Fumio
信州大学理学部附属諏訪臨湖実験所報告 9: 25-28(1995)
1995-10
http://hdl.handle.net/10091/1967
Rep. Suwa }lydrobiot, 9' 25b-28 (IP95)
Preceedings of the 7th International Symposium
an River and Lake Enitirenments, fPP4, Matsumoto
25
Eulchas incisicollis (Coleoptera: Eulichadidae), an important
decomposer of leaf litter in Asian tropical stream communities
Fumio HAYASHI
Department of Biology, Tokyo Metropolitan University, Minarniosawa
1-1. Hachioji, Tokyo, 192-03, Japan.
ZN[ffRODUCTION
Coleoptera is the largest order of insects, and its approximately SOOO aquatie mernbers make up one of the major groups of
freshwater arthropods [1]. However, inhabitants in the swifter
portions of streams and rivers are rare and, in general, small in
body s±ze [1]. However, there are exceptions. A North American
ptUodactylid. Stenocolus sp. is an extremeiy iarge coleopteran
(14-22 mm ±n adult body kength) living in stream riffies dur±ng
its larval stages [1]. In Southeast Asia, Euttchas, the oniy
genus of Euiichadidae, are large coieopterans w±th aquatic iarval
stages [2]. However, no information is availabie on their iarval
morphology or life cycles. Xn this paper, some bionomicai data of
E. incisicollis Pic, 1933 are presented.
METKOPS
The study site (200 ra iong) was located at a tributairy (stony
stream, altitude 200 m) of the Gombak River near the Field Study
Center, University of Maiaya, iocated in UXu Gombak, Selangor
Darui Ehsan, MaXaysia. and was vis±ted five ℃imes: 5-11 September
i992, 9-11 February 1993, 6 June 1993, 27 Septemberc-10 Octoberc
1993r and 19 March i994. The larvae were collected with a hand
net (2.0 mm mesh) throughout the study site and, after the pro-
thorax length (Fig. i) was measured with a slide caliper to the
nearest O.05 mrn, they were reieased at each coliecting point.
Stream temperatures were taken at noon one to three times at each
visit.
Six large larvae were reared in a laboratory aquariurn (20 X 30
em2 , 7 cm in water depth). The water was continuously aerated and
kept a℃ 23-250C (14 h ligh℃: 10 h dark). Small pieces of carrot
were g±ven as larval food. A giass box (7 cm in diameter) containing wet peat moss was placed in the aquarium for the larvae
gx2?ugstgth x2･sxge2.gdggg2.:ege, :ill?･Esd.gg g.ggggsi:,2flge.t20,g,,gR
twigs and leaves. They were also given a roughiy 10 & sugar
solution containing a iittle fermented mRk. .
0n 8 October 1993t nine larvae werce fixed in 70 g ethanol
immedlately after coXiection and laterc dissected. The whoie gut
(foregut to hindgut) and the body were separately dried at 80eC
for 12 h to estimate the dry weight ratio of gut contents to the
gutted body. AIX gut contents were identifted under a binocular
m±crcoscope (X20) after dissection.
26
x.ut
ge L
K'
.t tt.as
Mre
'''iv'L
g ;'
t.t.
ee bl-
.eq.sckl,ew
'
x.
FSg. 1. Larvae (left, dorsal; center, lateral view) and adult
fernales (righ℃, dorsaO of Eulichas incisicoZlis. The
coin is 23.5 mm in diameter. PL: prothorax length.
The density of Eulichas larvae in the study stte was estimated
on 30 September 1993. rn ℃he riffles, stones were sarnpled individual!y by washing thern in a net (O.20 mva mesh) held immed±ately
downs℃ream. Stones were weighed to the nearest O.Ol kg using a
spning ba!ance. and their sutface areas were laterc estimated by
the foxiowing equ stl.O?4532o] k w + ssg.4)O･667,
where s (cra2) is the surface area of the stone and w (kg) its
weight. The larval density per untt of stone surface was then
calculated.
RESULTS
Of nine laboratory-reared larvae, only one feraale adult (Ng.
1 right) emerged after the 17-day pupal period. This female left
the pupating space in the peat moss after another 11 days, and
iived forc 112 days in the cage. The body was brown coioured, and
34 mm in total length and 12 mm ±n width at the widest po±nt.
Eggs removed from this unmated female were white and eliipsoidal,
O.70 mm (Nxx5, SE=O.Ol) long and O.58 mm (N=5, SE=O.02) wide.
Larvae (Fig. ! Xeft) were found under and among stones at the
center of riffles. They were brown in body coiour and had many
fUamentous gUls on the ventral side of the abdomen. When stimukgxgge. tcgg ?g2t,xgeg'E.Rgd±'g;,gggg(.l.,gg"g2!.Bl,"e .x2an..k2gx%
consisted of only small pieces of failen leaves which were fuliy
27
Frequency
7
05
6
ff
AE
v=
5
ts,
mc
4
xes
"o
3
￠
sc
2
.v-,
o
u
A
1
Ao
o
di
-. 26
x
f
N
･s.･"
E ts 24
es
co
"
w
co
FSg. 2.
E"
w 22
ee
ee
ge
@
×
ov
@/
g-.
ee
J F M A M J J A S O N D
Seasonal ahanges in frequency distributions (number of
individuals) of prothorax length of larval Eulichas
incisicoZ2is. Samples were taken on 5-11 Septembezr 2992
(Nma23), 9-11 Februairy 1993 (N=26), 6 June 1993 (Nma44),
27 Septemberc-10 October 1993 (N=I07), and 19 March 1994
(Nm16). Annual st]rearn temperature regime is also shown
on the bottofn and the Une Xs drawn at 24"C.
packed from foregut to hindgut. The mean prothorax Xength of nine
Xarvae used for guic coRtent analysis was 4.33 mm (range 2.75-5.60
mrn), and the mean gut/body ratio was 29.i& (range 20.5-45.3&).
Annual strearu temperature was nearly constant at 240C, and all
sizes of Xarvae were found throughout the year (F±g. 2). In this
study, howeverc, srnaU larvae may have escaped capturce due to the
coarse mesh size of the coilecting net (2.0 mm). The size of the
first-instax iarvae and the numberc of instars were unknown.
DXSCUSSION
Adult E. incislco2Zis probably appear in all seasons, since
the large larvae were collected throughout the year. The larvae
inhab±ted stony niffies at a density of I.4 /rn2. They consumed
dead ieaves which accumulated ±n the gut, reaching nearly 30& of
their body weight. Although there are no comparetive data of
other species of leaf decomposers inhabiting tropical streams, E.
incisicoZlls is cons±dered to be one of most important decomposers.
28
zn East Asia, the reiative abundance of Coleoptera in stream
riffle benthic communities tends to increase from ternperate to
tropicai regions, and iarge-sized species such as EuZichas spp.
are found onky in tropical streams [2, 4]. Lotic members of
aquatic coleopteirans (Psephenidae, Pryopidae, Elmidae, Ptilodacty!±dae and so on) are generaliy detrit±vores [1] as is E. incis-
ico2lis. Therefore, as fallen leaves decompose on ehe stream
beds,
cokeopterans
probably
play
a more ±mportant
ro!e in a
tropical
riffie community
than in
a tempeacate
one.
Adults of E. incisic.o22is were rnuch karger than those of the
North Araerican Stenocolus sp., which is known as one of the
largest riffle--dwexxing coleopterans [1]. The environment of the
studied stream is charaeterized by (O constantly high teinpera-ture. (2) stabXe flow regirae because of its location in a weli
preserved hUl forest, and (3) no seasonal deficiency ±n falien
leaf raaterial. In such an environment, ±n contrast to ternperate
s℃rearas where temperatures decrease in w±nter and fallen leaves
are generaily unavailabie frora spring to summer, growth in trop±cal streams is unlnhibiiced by faUing temperatures orc food shortages. This is one possible reason why E. incisicollis has a long
Zarval perlod and subsequently rnatures to a large body size.
AC KNOptLEDGEMENTS
I wish to thank H. S. Yong (University of Malaya) and the
staff of the Field Study Center of the University of Malaya forc
their kind suppert ef ℃h±s study. X am grateEuX also to M. $ato
(Nagoya Women's Univexsity) for species identSfication of the
aduk specimen, and Y. Okush±ma (Kurash±ki Museum of NaturaX
Histo]ry) for usufu1 inforaiation regarding this spec±es. Th±s
study was partly supported by the Shikata Memeriai Trust ￡or
Nature Conservaston, Tokyo, Japan.
REFERENCES
1.
2.
3.
Whi℃e, D.S., Br±gham, W.U. and Doyeft, J.T.. 1984: Aquatic
Coleoptera. Xn "An Xntroduction to the Aquatic Xnsects of
North Aivierica" (eds. R.W. Merritt and K.W. Curnwins), pp.361437. Kendali/Hunt PublS$hing Company, Iowa.
Bishop, J.E., 1973: Limnology of a Small Malayan River Sungai
Gombak. 485pp. Dr. W. Junk B.V. Publishers, Whe Hague.
Kayashi, F., 1988: Mfe histoiry variation in a dobsonfly,
protohernies grandis (Megaloptera: Corydalidae): effects of
prey availabiMty and temperature. Frceshwater Biol., 19: 205216.
4.
Hayashi, F., unpublished data.

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