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Sexual dimorphism in the cocoon color of Bombyx mori (Bombycidae) PDF

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Preview Sexual dimorphism in the cocoon color of Bombyx mori (Bombycidae)

350 Journal of the Lepidopterists' Society mm versebars outlinedinblackand are only4 inlength. Neitheragentis expectedto ef- fect complete control ofM.faya because offayas exceptionallyinvasive traits such as its ability to fix nitrogen, rapid growth rate, and high rate ofseed production (Vitousek & Walker 1989). Literature Cited Davis, C. & N. L. H. KRAUSS. 1962. Recent developments in the biologicalcontrolof J. weedpestsin Hawaii. Proc. Haw. Entomol. Soc. 18:65-67. Deschka, G. 1976. Lithocolletidaevon Madeira(Lepidoptera). Entomol. Ber. 36:90-96. Gardner, D. E., G. P. Markin & C. S. Hodges, Jr. 1988. Survey forpotential control agents forMyricafaya in the Azores and Madeira. Technical Report 63. Cooperative NationalParkResources Studies Unit, Dept. Botany, Univ. Hawaii, Honolulu, Hawaii. 18pp. JULIEN, M. H. (Ed). 1992. Biological control ofweeds: aworld catalogue ofagents and theirtargetweeds. CAB International. 186pp. KLIMESCH, L. V. 1970. Caloptiliaschinella Wlsghm. (1907) (=C. terebinthiella Chret. J. 1910) (Lep., Lithocolletidae). Nachricht. Bayerisc. Entomol. 19(5):84-89. Markin, G. P. 1991. Insectsurveyofpotentialbiologicalcontrolagents ofMyricafaya in the Azores and Madeira Islands, Portugal, 1988. Technical Report 75. Cooperative NationalParkResources StudiesUnit, Dept. Botany, Univ. Hawaii, Honolulu, Hawaii. 26pp. Markin, G. P., R. F. Nagata & D. E. Gardner. 1991. Biological control ofintroduced weeds ofnative Hawaiian forests. In Conrad, C. E. & L. A. Newell, (Tech. Coordina- tors),ProceedingsofthesessionontropicalforestryforpeopleofthePacific,XVIIPa- cific Science Congress (27-28 May 1991) Honolulu, Hawaii. Gen. Tech. Rep. PSW- GTR-129, Albany, California: Pacific Southwest Research Station, Forest Service, U. S. DepartmentofAgriculture. Takhtajan, A. L. 1980. Outline ofthe classification offloweringplants (Magnoliophyta). Bot. Rev. 46:225-359. TAYLOR, D. & G. P. Markin. 1992. Release ofa defoliator moth as abiological control agent of firetree in the park. Unpubl. environmental assessment for release into HawaiiVolcanoes NationalPark, Hawaii. 23pp. VITOUSEK, P. M. & L. R. WALKER. 1989. Biological invasion byMyricafaya in Hawaii: plant demography, nitrogen fixation, and ecosystem effects. Ecol. Monogr. 59: 247-265. WALSINGHAM, L. 1907. Microlepidoptera of Tenerife. Proc. Zool. Soc. London, pp. 982-983. Rosemary Leen and George Markin, U. S. DepartmentofAgriculture, Forest Ser- vice, Pacific SouthwestResearch Station, P. O. Box236, Volcano, Hawaii 96785, USA. Receivedforpublication20March 1995; revisedandaccepted 7January 1996. journaloftheLepidopterists'Society 50(4), 1996,350-353 SEXUAL DIMORPHISM IN THE COCOON COLOROF BOMBYXMORI (BOMBYCIDAE) Additional keywords: pupalcolor,voltinism. The mulberry silkworm, Bomhyx mori L., is one ofthe most commercially exploited lepidopteranspecies. Hybridsbetweencommercialsilkwormstrainsarerearedtoproduce Volume 50, Number 4 351 |BfHlH«BB MLAILGEHTCYOECLOLOONWS FEDMAARLKEYCEOLCLOOOWNS, jIff^ilXVY^1.*\"HQ'fc!. FlG. 1. Sexualdimorphism incocooncolorinBombyxmori. cocoons for rawsilkproduction. In the production ofhybrids, sex separation is necessary toprevent free matingbetween siblings. Inthe silkworm industryin India, sexseparation is basedon the imaginal spot on the lowersegment ofpupae, whichprovides reasonably reliable determinations but requires considerable labor (silkworm larvae have Herold's imaginalbudin males and Ishiwadas glandin females on theventral side ofthe 8th and 9th abdominal segments; similarvisible external characters are known in Saturniidae; see Milleret al. 1977, Miller& Machotka 1980). Pupal sexingalso requires cuttingopen co- coons to confirm sex. In the preparation ofsilkworm hybrids, this method ofsex separa- tionbecomes expensivewhen reciprocalcrosses are notdesired. Severalstudieshavebeenconductedonsexdeterminationinparentalracesatdifferent developmental stages in silkworms (Tazima 1978a, 1978b, Abadzhieva & Tanev 1987). Sengupta (1968) reported sex-limitedcharacters oflarval markings in a Russian silkworm race. Krishnaswami et al. (1981) observed sexual dimorphism in cocoon color in Hosa Mysore, a multivoltine silkworm race. Nagaraj and Rao (1987) succeededin introducing sex-limitedcocoon colorintobivoltine silkworm races CC1 and NB4D2. However, these characterscouldnotbecommerciallyexploitedowingtothelowsurvivorshipandstability intheseraces. Inthepresent study,we attempted to fixabreedingline from abackcross of(Mysore local x N4) x Mysore Localwith sexual dimorphism in cocoon colorto facilitate the pro- cess ofhybrid silkworm seedproductionin commercial grainages with minimalwastage. Segregation oflines was made after the F3 generation. In one ofthe sub-lines cocoon colorwas found to exhibit sexual dimorphism. Studies ofthe sexual dimorphism began with random cocoon samplingfrom fivebatches. Lightyellowanddarkyellowcoloredco- coons were separatedvisuallyinto groups. These cocoonswere then cut open and sexed onthebasis ofpupalmarkings. Thisattempttoclassifycocconswas repeatedfourtimes. In an isolated sub-line from the threewaycross of(Mysore local x N4) x Mysore Lo- cal, sexual dimorphism in cocoon colorwas observed in the F12 generation (Fig. 1; male cocoons are lightyellowin color, whereas female cocoons are darkyellow). Invisuallyse- lectedlightyellowcocoons 96.5% were male and in darkyellowcocoons 92.5% were fe- 352 Journal of the Lepidopterists' Society TABLE 1. Results ofattempts to segregate Bombyx mori cocoons bysexusingcocoon color. CocoonColor SampleSize Replications PercentMale PercentFemale lightyellow 400 4 96.5 ± 4.7 3.5 ± 4.7 darkyellow 400 4 7.5 ± 9.6 92.5 ± 9.6 male(Table 1).Thefemalecocoonsweremoreelongate,lessflossyandslightlylargerthan the malecocoons. Slightlyoval, spindle-shapedcocoonswerecommoninbothsexes. Tazima (1978a) has explained the phenomenon ofdifference in cocoon colorbetween sexes and reported that cocoon colorin most ofthe colored cocoon producing silkworm racesisdirectlyrelatedtohemolymphcolor,exceptinsome Europeanraceswheretheex- pression ofcocoon coloris influenced by an inhibitor gene. The presence ofthe yellow blood gene (Y) in silkworms is responsible foryellowcolorin cocoons. The allele +C in- hibits transmissionofpigmentsinto anypartofthe middle silkgland, resultinginproduc- tion ofwhite cocoons in some silkworm genotypes. Presence ofY and +C alleles in tan- dem is stated to be responsible forintermediate color in cocoons and polymorphism in hemolymph color (Tazima 1978a; Ford 1975 reported that hemolymph color is always darkerin females thanin males ofChoristoneurapinus (Tortricidae)). Itisinterestingtonotethatthe coloredcocoonproducingraces ofBombyxmori in In- dia, such as Nistari (golden yellow) and Mysore Local (greenish yellow), do not exhibit clear sexual dimorphism in cocoon color. However, use ofthese in the formation ofnew racesthroughhybridizationresultedinsexualdimorphismintheisolatedsub-lines (Krish- naswamy et al. 1981, Nagaraj & Rao 1987, Singh et al. 1992). Similarly, in the present study, two parental races (Mysore Local multivoltine race with greenish yellowcocoon, and N4bivoltine racewithwhite cocoon)were combinedin athreewaycross toobtain a breedinglinewith sexual dimorphism incocooncolor. The relativeimportance ofgenetic and environmental factors in the expression ofsexual dimorphism in cocoon colorcould notbe determinedin the present study. Furtherworkis ongoingto obtain detailedinfor- mationon sexualdimorphism andits relationtoclimaticandotherecologicalconditions. We thank S. Sekar, stenographer of the Regional Sericultural Research Station, Coonoor fortypingthis manuscript andto the technical staffwho assistedinthe comple- tionofthis study. Literature Cited Abadzhieva, R. & G. Tanev. 1987. Agenetic markerforsexinthe silkworm. Genet. Sel. 19:535-538. Ford, E. B. 1975. Ecologicalgenetics. Chapman& Hall, London. 173pp. Krishnaswami, S., M. N. S. Iyengar & S. N. Malavathy. 1981. Cocoon colouras anin- dication ofsex in Hosa Mysore, an evolved silkworm, Bombyx mori L. Proc. Seric. Symp. Semi. 18-20. Miller, T. A., W. Cooper & W. Highfill. 1977. Determination ofsexin fourspe- J. J. ciesofgiant silkworm mothlarvae (Saturniidae) Lepid. Soc. 31:144-146. Miller,T. A. & S. V. Machotka. 1980. Sex-relatedJm.orphologicalcharactersinlarvaeof HyalophoragloveriandAntheraeapolyphemus (Saturniidae). Lepid. Soc. 34:69-73. NAGARAJ, C. S. &R. M. Rao. 1987. Newsletter, Central SericulturJa.l Research &Training Institute, Mysore. 2:3. SENGUPTA, K. 1968. Sexlinked (sexlimited) characters intwo races ofsilkworm Bombyx mori L. maintainedbythe Central Silkworm Seed Station, Srinagarand the method Singfho,riKts.,trTa.nsPf.erS.toCohtaheurhraances&foMreceomrmaerVceiramlae.xpl1o9i9t2a.tioSne.xuIanldidanimJ.orSperhiicsulm.i7n:7c9o-c85o.on colourofsomemultivoltineandbivoltinesilkworm (Bombyxmori L.)ecoraces. Indian Entomol. 54:365-367. J. Volume 50, Number 4 353 Tazima, Y. 1978a. The silkworm - an important laboratory tool. Kodamsha Ltd., Japan. 307pp. . 1978b. The silkworm egg. CentralSilkBoard, India. 49pp. V. Thiagarajan, T P. S. Chauhan and E. Rajalakshmi, Regional Sericultural Re- search Station, Central Silk Board, Coonoor-643 101, TamilNadu, India. Receivedforpublication 30June 1994; revisedandaccepted 7January 1996.

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