Table Of ContentTThhee LLeepipdiopdteorpoltoegircaollSoocgieitycal Society ooff JJaapapnan
uetma 7'reiiblse,pid.Soc.Jkepan61 (3):218-220,O2c0t10
A note on the male-specific size reduction of head capsule width during the last
larval molt in the wing]ess bagworm moth Eumeta variegata (Snell e18n7,9)
(LepidoptePrsyac,hidae)
ShuheiNiETsu*
Department ot' Lit' eScience, lnternation aClhristian University ,Osuwa 3-1O-2, Mitaka. Ibkyo 181-
858S,Japan
Abstract This short note dcmonslrates the moiphological evidence of male-specific size reduction
of head capsule width during the las t)arvaHnstar of the bagworm moth Eumeta i:ariegata (Snellen.
1879) I.n this species, sexuat dimerphis mappears in the las tlarya sltage, with tlt emale larva ebeing
smaller than female larvae .Head capsule width in the t'emal eincreas eafster the las tlarva lmolt, whi]e
in the male head capsule width is reduced in the las ltarva ilnsta Trh.ese results shosN' that the reduction
of the epicraniaL plate causes the size reduction of head capsules during the las tlarva linsta rin mates.
This is the fir sdtescripti oofn the proces sof the male-specific size reduction ofhead capsule width in
lepidoptera ninsect sduring the las tlarva lmolt.
Key words head capsu]e width, sexual dimorphism, bagworm moth, Eumeta varie,gata.
In all arthropods a series of ecdyses divides the lif espan of the animal int oa series of stages,
while the anima] itsel fappears as a series of instar s(SnQdgras 1s9,35). When the cuticle is
formed ,the integuments allows ordinary size increas (eSehn a1 9l8,5) .In the larvae ofLepidoptera
only the head capsule and it spart sare heavil ysclerotized. However, it is known that some
Lepidopter raeduce the size of their head capsule in late rinstar wshen compared with preced-
lng lnstars,
The female-wingle sbsagworm moth Eumeta variegata (Snell e18n7,9) is an importan tpest
of shade and ornamental trees and shrubs in western Japan (Nishid 1a9,83) ,Last insta lrarvae
are sexually dimorphi cth;ose of female asre blac kwith head capsule widths averaging 4,9
mm, while those of males are pale yellow-brow nwith head capsule widths averaging 3.4 mm
(Se eNishida, 1983; Fig, 1a) .The presen twork emphasizes the detaile mdorphological differ-
ences and the size reduction of the head capsule width in male E. variegata larva ebetween
the penultimat (e7th a)nd fina l(8th i)nstar F.emaie 8th insta lrarvae have a larger head capsule
than that of the 7th insta rwh,ile male 8th instt tlrarva ehave a smal]er head capsule than that
of the 7th insta T(Fig .Ib), In the last insta rof male E. variegata larvae ,the fronta lsuture is
milky white while the head capsule is dark brown. In the penultimat iensta orfmaie larvae the
head capsule is reddish brown (Fig .Ib) .In spite of the size reduction of the head capsule in
male larvae ,the size of the clypeofrontal plat ein the last insta rwas similar to that of the
penultimat iensta rT,he width ofthe clypeofrontal plate was about 1.6 mm in both the las tand
penultimat ienstar (sFig 1.b, white arrows). Interesting tlhye, reduction of the epicranial plate
was easily detecte dfrom the penultimat einsta rto the las tinsta r(Fi gI.b, red arrows). I
speculate that that the size reduction of male head capsules is correlated to the reduction of
adductor muscles of the mandible which occupy most of the later aplarts of the head cavity,
"E-mail: [email protected] .jp
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Reduction ot' head capsule width in Eumeia variegata 219
ee:,/.diptit ,.-･ilg".wy/.pa
t t titt wt lit
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!f ,, {,li ,..tw,x.tif'
/t/tl iv./,/g/'
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Fig, 1.Head capsules of the larvae of Eumeta variegata. Scal ebar: 2mm.
a. Thc fina (lgth )insta orf femal e(upper a)nd male (lower 1)arvae.
b. The penultirnat e(7th i)nsta rof male (uppe ran)d of the fina ](8th i)nsta rof male (]ower)
laryae .Note the smaller head capsule of the 8th male insta rcompared to the 7th male instar.
White arrows indicat ethe width of the clypeofrontal plate .Red arrows indicat cthe epiera-
nial plate.
This phenomenon might be due to larvae not feeding during their winter diapause H.owever,
these speculations cannot be applied to female larva edue to the enlargement of the head
capsule during the las tlarva mlolt.
As mentioned above, the external morphology of the las tinsta rlarva eof the male is quite
differe nftrom that of it spenultimate insta rL,arvae of the firs tto the penultimat einsta freed
on plan tmaterial, but the eighth insta ris a quiescen nton-feeding stage, Pupation takes place
in the case during mid April and the adults emerge from mid-May to late-Jun ei.n the same
year,Reduction
of head capsule width in Lepidoptera is known to occur in other species. Kuroko
(1987 )describe dsize reduction of the head capsule in the las t(4t hi)nsta orfAntispila uenoi
Kuroke, while Lee et al. (2006 r)eported a similar situation in the las t(7th i)nsta orfAntispita
disoTtet Lteae et al. Maier (1988 n)oted a similar situation in the las t(5t hi)nsta orf the North
American species Coptodisca negligens Braun. These size reductions may be related to the
non-feeding behavio rof fin ailnsta lrarvae b,ut Wani et at. (1994 )reported a special case of
head capsute size reduction caused by parasitism .Their results suggest that the reduction of
the head capsule widths of parasitiz ehdost larva eof Galleri amelionella (Linnae uwass)
caused by the parasito iAdpanteles gaUeriae Wilkinson (Hymenopter aBr:aconidae) larvae,
The presen tpaper has describe dan obvious case of male-specific size reduction of the head
capsule width in larva eof E. variegata. In order to understand this phenomenon, furthe srtud-
ies on the adaptive significance of the moiting proces sand on the behavio rof E variegata
larvae in their fina linsta rwill be needed.
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220 Shuhei NIITsu
Acknowledgments
1 thank Dr lan Sims for his useful comments in preparin gthe manuscript and for his ¢orrect−
ing my English，
Refe
『ences
Kuroko． H．，1987． Three new sp巳cics of the genusAntispila（Lepidoptera；Heliozelidac）from亅apa11 ． Tinea 12
（Suppl．）：109−117，
1．ee， BW ．， Hirowatari， T． and H， Kuroko，2006． A ncw species ofAntispila （Lepidoptera：He［iozelid）tftrcom the
Mai erR， yCuk Ty．u，s，1 9J8a8p． aLn，i wfiet hcy cdlees cofri Cpotipotn osodfi isicn nameagltiugernes stagc（sLe．p Aindnop． teentra， ：SHeolci， Aomzel．i9d9a：）e1on01 c9−ra1nb0er2ry7．訊 ec・oη． Ent．
81；497−50｛，． ’
Nishida， E ，1983．Biologies and parasi tcoemplexes of two bagworms ， Eumeta ／aponica and Ei‘niata tninuscule
（Lepidoptera， Psychida¢），in亅apan ． Kont），i251 ：394−41L
Snodgrass， R． E．1935， Principle sof Insect Morphology ，667 pp． CornellUnivers Pirtcyss．
Sehnal， E 1985．Comprehensiv einsect physiology， biochemistry， and PharmacolDgy． vol．2． Pergamon ， Oxford．
Wani． M ．， Iwabuchi， K， and J， Mitsuhashi，1994． Dcvelopmental responsesof α↓’leri maelloneUa （Lepidoptera，
Pyralidae）1arva teo parasiti sbmy a braconi dparas電oiid． Apantetes ga〃eriae （Hymenoptera ， Brac〔midac ）．
Appl． Ent． Z〔丿o’．29：193−201．
摘 要
オオ ミノ ガ（鱗翅 冂，ミノガ科）における幼虫期の最終脱皮に見られる雄特異的な頭幅サ イズ
一
の縮小に関する 知見 （新津修平）
著者は オオ ミノガ雄の亜終齢幼虫期か ら終齢幼虫期に見られ る頭幅サ イズの縮小過程につ い て，そ
，
の幼虫の頭部形態の比較観察に基づ き，若干の考察を行っ た．1995年に東京都 こ鷹市内で採集した若
齢幼虫を東京農業大学昆虫学研究室におい て飼育し，材料 として用い た．雄の亜終齢幼虫の脱皮殻と
終齢幼虫の頭部を解剖 し，観察を行っ た．これまで，Nishida（1983）により．雄の亜終齢幼虫期か ら終齢
ー
幼虫期における頭部サイズの縮小につ い て 多数の個体を用い た続計学的なデ タに基づ く報告が な
されてい る．本研究では．雄の亜終齢幼虫期か ら終齢幼虫期にかけての頭部前面の形状を初めて図示
し，比較観察を行っ た．その 結果，雄における頭幅の縮小過程におい て，雄の亜終齢幼虫期と終齢幼虫
期の額頭楯板 （clypeofrontal plate）a）幅に縮小は見られなかっ た．この こ とから雄の頭幅の縮小は，頭
蓋板 （epicranial plat）eの サイズ縮小の結果起こることを．比較観察の結果か ら今同初め’て明らか に し
た．この 雄に見られる頭蓋板のサ イズ縮小に より，幼虫頭部の大顎か ら頭蓋板に 引き付けられる内転
筋（adduct r musc ］es）の iJ少dがi推察された．その背景として，オオミノ ガの幼虫が雌雄共に最終脱皮 し
てから蛹化 まで 摂食を停止する行動 との関連性が示唆された．一方雌で は，亜終齢幼虫期か ら終齢幼
虫期にかけて脱皮するこ とにより．頭幅サイズは増大 し，幼虫の サイズ も大きくなる 、本研究で は，終
齢幼虫期における雌雄の 幼虫の サイズに大 きな性的な差が見られるこ とを，雌雄間における頭幅サ イ
ズの縮小と発達 とい う点か ら．比較観察と考察を行っ た．
（Received亅une 2，2010、 Accepted June 23，2010）
Published by the Lepidopterologica lSociety of Japan，
5−20，Motoyokoyama2，Hachiji，Tokyo、192−0063Japan
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