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uttwh 7hans ZgpidSoa Japan 54 (2):125-130.March 2003
Aerial dispersa lbehayior and positiv ephototropis mof hatched
laryae of bagworm moth, Eumeta minuscula (Lepidoptera,
Psychidae)
Shintar oFuNAKosHI and Hiroyuki TANAKA
Ohgakikita High School,Nakagawa-cho 4-110-1,GifuPTefi5,03-OO17Japan
Abstract Experiments were carried out to examjne whether the balloonin gefhatched larvae
was efi'ected by larval phototropisrn and velocity of ajr. The orifice of the case was directed
downwards and li tfrom beneat hby an electric torch in a dark roorn. Many hatched larva eof
the bagworm morh, Eumeta minuscula Butler ,crawled down into the orifice of the case and
disperse don spinning cobwebs. The velocity of air had no eifect on dispersal rates.
Key words Bagworm moth, aerial dispers ablehavior ,hatched larva ,positive phototropism.
Introduction
Male imagoes ofthe bagworm meth have wings and can fly lik eother moths. On the other
hand, female imagoes ,whose forms are larva ltypes, have no wings, They cannot fl yand are
in bags throughout their lif e,The late rinsta rIarva eofbagworms have excellent abilities in
movement, and are often crossing streets and under the eaves ofbuildings. They have been
locate din isolate dareas where it seemed impossibl eto crawl, for there were wide streets or
city waterways hinderin gthe route (Wakazon o& Funakoshi, 2002), As the bags were fbund
at the place where they had never been seen in the previou syear ,i twas suggested that aerial
dispersio nor, ballooning by the hatched larva eoocurred. Previously ,there have been sorne
investigati oonns the balloonin gof bagu･'orms (Mar c& Gerhard, 1977 ;David et al., 1986),
However, litt lies known about the ballooning and dispers albehavior of the hatched
bagworm 1anrae in Japan. The objective of our study was to investiga ttehe etfect on
balloonin gof larva lphototropis mand velocity of air,
Materials and methods
About fift hyatched larva eof Eumeta minuscula were put in a semitransparent plasti ccase
(8.0c mhigh, 24,2cm2 diam.) . This case was put in fron tof an electric fan under three
conditions, i e. (1 )the orifice of the case was directe dupwards in a li troom, (2 )the orifice
was directe ddownwards in the same room, and (3 )the orifice was directe ddownwards and
li tfrom beneath by an electric torch in a dark room, Piece sof white paper, measuring 1×
5 m2, were spread in fron tof the electric fan and a white curtain measuring 2× 1. 9m2 hung
at a point 5m from the fan . Air was blown against the plasti ccase fbr seven minutes on
each of the fan' sthree settings, and the number of disperse dand stationary individua lwsas
recorded. The hatched larvae ,which had been carried off by the air ,were searched fbr on
the white paper and curtain. The flyin gdistanc ew,hich the individual hsad traveled ,was
measured from the case to the paper and curtain,
The filt epraper ,on xlp'hich approximately fift hyatched 1arva eof El minuscula were p]aced,
was set up vertically and li tby an electric torch from 3 directio nosf lef tr,ight and down in
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126 ShintaroFuNAKOSHIand Hiroyuki TANAKA
vr
Fig. 1 . Hatchec lbagworm larva ecrawl down into lightin dgirectio fnrom beneath with positive
phototropism.
Fig.2. Hatched bagworm larva ecrawled on the circumference of the case in the li troom
and bailooning did not oecur.
Fig. 3. Aerial dispersal behavior of hatched bagworm larvae.
Fig. 4. Ditto ,magnified.
a dark reom (Fi g1.) , To measure larva lcrawling ability downwards, the crawling velocity
of larvae was measured from the center to the edge of the paper and recorded by a video
camera Also hatched larva ewere put in the same conditions in the dark room. The
experiments were car'ried out in July ,2001.
Results
Table 1shows the rates of dispersed1arvaeof Et minuscula under the three conditions.
Table1. The rates of dispersa llarva of Eumetaminuscula at the three condition (%).
orifice upwards downwards downwards"
stage 1stage O (50) O (50)O 66.0 (50)
2stage 3.7 (40) (38)O 61.9(42)
3 O (S2) (52) 66.1 (59)
*Lighting from beneath by an electrictorchin the darkroom.
( ) :number of larva eused.
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Ae-al Dispersal Behaiior and Positive Phototropism of HdtLhed Ldrvae of Bagworm Moths 127
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AsExh!;
g;.
Stage 1
"-"--
"Stage 2
o Stage 3
g l2345 5
Olstsnoofm)
gls
i
!
NStage 1
-Stege 2
M$tage 3
og vsoT k-T` " ro to ede s t?s
sg$ as $xs$
m q' `DDistence(`m")
Hg 5 Atr velocity at thiee stage at the six pomts at rnteivals from]ust in fion tof the fan
big 6 Flying distanc eof hatched larNa of Eumeta minuscuta
Almobt none of the hdtched larva efiew from the case in the 1i troom When the onfice ot
the case was directe dupwards, hatched 1arva ecrawled on the circumference ofthe case (Fig
2) When the onfice of the case was directe ddownwdrds, hatched larva ecrawled up the
semitransparent case and wandered around on the bottom On the other hand, when the
oiifice of the case was directe ddownwards and 1i tfrom beneath by an electnc torch in the
dark room, dlmost all of the hdtched larvd ecrawled down into the orifice of the case and
about 60% of all hatched larva espun cobwebs and flew (Fig 3s, 4) The velocity of air had
dispersal
no efTect on rates
The arr velocity wag measured dt six point intervals from just in fron tof the fai iduring the
three stages The air velocitieb were differe nmt each ofthe three stages In the third stage,
it was 23 tirnes as larg eas it wds at the firs sttage in fron tof the fan ,whereas 5 m from the
fan, it was 1 1 5 times as larg e(Fi g5) The flyin gdistance osfhatched larva eofE minuscula
are shown in Fig 6 Though hatched larva edisperse tdo a greater distanc eon the strong air
of stage 3, the numbers of disperse dIarvae were almost the same for the three velocities ofair
Fig 7 shows the crawling velocity ofhatched larva eon the vertical filt epraper when ht from
three directien s Every hatched larva crawled at almest the same velocity towards the
hghtmg directio n The differenc eofsvelocity between right (1 139±O]75 mm/sec n=50)
,
and lef t(1 152±O 152 mm/sec n::= 50) were not evident statistically On the other hand, the
,
downwards velocity was slower (0 939± I 183 mm/sec n=50) The ditferenc eofscrawlmg
,
velocity between down and mghtlleft were significdnt stdtistically (t-te sPt<O,oo1)
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l.S
1.4cox
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O.8sto
O.6oT
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O.2
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Lsk Right Down
7
Light ciirec ttevvards
10
ee
8
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U LV L OL D RO R RU
8
Direat tQwards
Fig. 7. Velocit yoferawling ofhatched larva etowards lightin dgirectio n.Means ±SE velocity
of 50 hatched larvae crawling towards the lighting direction.
Fig. 8, Directio nof crawling of hatched lan･'a oen the vertical filt epraper in the durkroem,
Around 50 hatched larvae crawled towards the directio nfor 3 minutes in the
darkroom (U :up, L: lef tD,: down, R: right).
The crawling velocity of hatched larvae on the vertical filt eparper in the darkroom was
slower than in the case towards the li tdirectio n.The crawling velocity ofhatched larvae in
the darkroom changed from O.17 mm!sec. to O,46 mm/sec. The direction sofcrawling were
ditlere natnd changed rapidly in dark conditions (Fi g8.) . It was not recognized to be
negatlve geotroplsm,
Discussion
Spider sstand facin gthe wind and squeeze out a drop of silk which is expanded furthe rby
the wind. When the pull on the threads from the air currents is strong enough, the spider
will fioa toff into the air, As spiders have no wings, aerial dispersa lin these animals is
commonly known as "ballooning" (Deca e1,978; Yoshikura, 1987), The larva eofbagwor-
ms, the female of which cannot fiy ,might also dispers eon the wind by spinning like a spider.
But few hatched larva efiew on the air and it did not seem that they were able to fi yactively.
Fortunately, we fbund that right after eclosion, larvae have a strong positive 'phototropic
inclinatio n.Then, in the darkroom, a case containing the larva ewas turned over and
illuminate fdrom below, then put in front ofa fan . As a result, about 60 percen tofthe laryae
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Aerial Dispersal Behavior and Positive Phototropism or Hatched Larvae of B乱gworm Moths l2g
were on the air fbr seven minutes ． The fbrce of the air did not have much effect on flyjn．g
Even on gentle air， in the firs sttage hatched bagworm larva ecan spin cobwebs and disperse
，
on them ．
Air velocity fall sas the distance倉om the fan in the room increase， swhereas wind velocity
does not 齟 in the 且eld ． Wind speed stays regular at certain hours． It was thought that the
wind brought hatched bagworm l arvae to their resp tive distance． sIt was estimated that
hatched bagworm larva edisperse dwithout having to wait 鉛r strong winds ， b ause air
moving slowly seemed to be enough fbr flyin，g
Nishida（1983）mentioned that probably positiv pehototroplsm allows the larva teo move in
the ligh tdlr tion from the dark interio rof the pupal case and the bag． Through this
experiment ， it ls evident that hatched larva ehave a stronger positive phototropic inclination
than the negative geotropis mwhich characterizes many insect’sbehavior， Females lay eggs
on the top ofthe bag which are then closed insid ethe bag as a place fbr hatch｛ng ． Hatched
larva ecrawl down the orifice towards the ligh tand spin cobwebs for their fligh ftrom the bag．
However ， when lit丘om three directio nwse cannot understand why the crawling velocity of
hatched larva edownwards is slower than towards right and le丘．
Acknowledgements
We wish to express our sincere thanks to Ms Mika Sugim◎to Kyushu Universit yfor her
， ，
suggestions and sending much literatu． reWe also grate血11y thank Mr Hiroakl lkeda
，
Arachnological Society of Japan， fbr sending the literatu orne spiders． We grat血elly thank
Mr Christophe rBoon Ohgakikita High School f（）r corr ting the English． The present
， ，
study was supported by Grant−in Aid from Shimonaka Memorial Foundation ，
References
D a v ideρ， hLem． Ceo广Xaefo ramtnSd D（．L eAp，i Pdoopttteer，ra1：9P8s6y， chAiedraiae）．l diCsapne．r sEanl tb．eh1a1v8i：o5r2 5o−f5 l3a6r．vai bagwQrms ， η釜ア編 qρ酵γκ
Decae， EJ987 ． Dispersa lballoonin gand other mechanisms ． In Nentwig ， W ．（Ed．）， EcophysiolOg．ア （ゾ
Spiders；346−356． Springe−rVerlag， Germany ．
R h a inbadgsw， oMrm．， G rliarevs，a eG，ハ a抛nd励 P．ρ S伽． Cαhe（wWa，lk1e9r97）． （LAedpaipdotpitveer saig：niPfiscaynccehid aofe）． denCsaint．y −dEenp t．en1d2e9；nt 9b2a7l−l9o3o1ni，ng by
Nishida， E ，1983． Biologie sand parasite complexes of two bagworms， Eumeta ／Oρonica and Eumeta
minuscuia （Lepidoptera， Psychidae）． 」Konり痂 51：394−411，
Wakazono ， M ， and S． Funakoshi，2002． Internal conditions of bagworms of five large species． Trans．
勿ゴとt ∫o（r．ノOρan 53：63−68，
Yoshikllra， M ．，1987． The Biolog yof Spider．s 613pp． Gakkai Shuppan Sennta．（In Japanese），
摘 要
・
チ ャ ミノガ孵化幼虫の 空中分散 と正の走光性 （舩越進太郎 田中浩之）
雌が翅をもたない 幼虫型で，一生を ミノ の中で過 ごす ミノム シ は，幼虫の空中分散が知 られる．チャ
ミノガ Eumeta minuscula Butlerの孵化幼虫を使っ て幼虫分散 を観察 した．半透明の プラス チ ック容
器に ミノを作る前の孵化幼虫を入 れ，扇風機の風 を送っ て分散数や飛翔距離を測定した．暗室内で容
器の 口を下に し，下か ら懐中電灯の光を当てた場合，7分間で約 60％ の幼虫が分散した．それ に対し，
明るい部屋で容器を上に向けた場合，幼虫は容器の 口の周 りを回るだ けで あり，下に向けた場合は上
になっ た底に集まっ て，ほとんど分散は見 られなか っ た．孵化幼虫に とっ て負の走地性よりも正の走
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130 Shintar oFuNAKosH【and Hiroyuki TANAKA
光性が優先 した．約 50匹の孵化幼虫 を垂直に敷い たろ紙の．Lに置 き，暗室内で光を一方向か ら当て
ると，光の方向に向か う走光性を示 したが，下に 向か う幼虫の移動速度 （0．939±0，183mm ／sec．）は左
右 に向か うもの （1．139±O．175 mm ／sec，，1．152±0」52 mm ／s ，）より劣っ て い た．光源 をな くした場合
は個体に よっ て まちまちで，移動の方向は定まらず，負の走地性はみ られなかっ た．また，移動速度
も o．17 mm ／sec．か ら 0．46 mm ／sec．の 間で，光源に向か う速度に比べ て遅い もので あっ た，孵化幼虫
の走光性の 強さは，ミノの 口 は下に開口 してお り，ミノ上部で孵化した幼虫が 開口部に向か う こ とを
考えれば当然とい える，また．扇風機の風を 3段階に切 り替えて実験 を行っ たが，孵化幼虫の分散数
にはほ とん ど差がな く，ミノガ孵化幼虫は強風を待たずに分散 してい る と推測 された．飛翔距離は強
風の下で長か っ たが，自然界で は室内の扇風機の ように風源か ら離れる と風速が弱 まるこ とはな く，
弱風で も風 に乗っ て遠 くまで分散するもの と考えられた．しか し，それぞれの 方向か ら光 を当てた場
合，孵化幼虫が左右に向か うより，下に向か う方が遅い理由は理解で きなかっ た．
（Accepted OctQber 15，2002）
Published by the Lepidopterological Society of Japan ，
5−20 Motoyokoyama 2，Hachioji，Tokyo ，192−0063 Japan
，
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