Rearing experiments of Cx. tritaeniorhynchus Giles immatures were conducted under different temperature and densities to ascertain the developmental period and the mortality, which are parameters required to estimate the survivorship of natural populations. Linear relationship was confirmed between the rearing temperature and the developmental velocity, and the developmental zero was estimated between 11 and 15C. No instar specific or temperature dependent mortality was observed. The density effect was represented by the prolongation of immature period and by the increase of mortality. Higher mortality was probably due to longer immature period. The observed density effects might be caused by competition for food in old instar larvae

Maruyama Katsumi

Sugiyama Akira

Takagi Masahiro

Nagasaki University's Academic Output SITE: NAOSITE

Trop. Med., 38 (2), 69-77, June, 1996　　　　　　　　　　　　　　　　　　　　　　　　　　　　　69A Laboratory Experiment on the Larval Development ofCulex tritaeniorhynchus (Diptera: Culicidae) Giles underDifferent Temperatures and DensitiesMasahiro TAKAGI1, Katsumi MARUYAMA2, and Akira SUGIYAMA31Department of Medical Entomology, Institute of Tropical Medicine, NagasakiUniversity, 1 - 12-4 Sakamoto, Nagasaki 852, Japan2Dqpartment of Eφidemiology and Information, Mie Prefectural Institute of PublicHealth, 3-446仙34 Sakurabashi, Tsu 514, Japan3Dqpartment of Public Health, Faculty of Domestic Science, Nagoya Women'sUniversity, 3-40 Shioji-cho, Mizuho…ku, Nagoya 467, laφanAbstract: Rearing experiments of Cx. tritaeniorhynchus Giles immatures were conductedunder different temperature and densities to ascertain the developmental period and themortality, which are parameters required to estimate the survivorship of natural populations.Linear relationship was confirmed between the rearing temperature and the developmentalvelocity, and the developmental zero was estimated between 11 and 15C. No instar specificor temperature dependent mortality was observed. The density effect was represented bythe prolongation of immature period and by the increase of mortality. Higher mortality wasprobably due to longer immature period. The observed density effects might be caused bycompetition for food in old instar larvae.Key words: laboratory experiment, larval development, Culex tritaeniorhynchusINTRODUCTIONCulex tritaemorhynchus Giles is a main rice field breeder and is well known as a prin-cipal vector of Japanese encephalitis almost throughout Asia, where the rice cultivation verywidely prevails. Because irrigation for rice cultivation to provide sufficient amount ｡f foodhas been promoted world-widely, the medical importance of this rice field breeder has muchincreased recently. Many studies on this species have been reported, but we believe thatmore knowledge on the ecology is still necessary･ Especially, precise observation of the larval･developmental process is essential to confirm such population parameters as larval develop-mental velocity. The developmental period of immature stages, which should be required tocalculate the daily survival rate of the natural larval population, was examined by Wada andOmori (1971) and Mogi (1978) in Cx tritaeniorhynchm of Nagasaki population. The effects oflarval habitat conditions on the development of the species were also experimentally studied,Received for publication, silly 5,1996.Contribution No. 3336 from the Institute of Tropical Medicine, Nagasaki University.70the crowding by Nakamura (1979), the photoperiod by Yoshida et al. (1974), the biologicalconditioning by larvae by Nakamura (1978), and the larval density, the food shortage and thewater qua!軸by Siddiqui (1976)･ Discussion in detail on the immature population was madeby M咽i (197軌we conducted a rearing experiment of Cx. tritaeniorhynchus immature populations un-der different temperature and densities to ascertain the developmental periods of Mie popu一且ation of the species to prepare a basic parameter to evaluate the survivorship in the naturalpopulati｡ns. Results obtained are reported here.MATERIALS AND METHODS宜mmature stages used were derived from eggs deposited by blood fed females whichwere caught at cow sheds surrounded by rice fields near Tsu city, Mie Prefecture, centralJapan･ The area was described in detail by Takagi et al. (1995)･Two series of rearing experiments were performed. In the first experiment (experimenti), 100 larvae hatched within 12 hours were placed in a plastic jar of 20×30×5cm in size,under three varieties of water temperature (22, 25 and 28C). Larvae were examined for theirlnstar at 12 hours interval. When the new instar larvae were found, only they were removedto another jar of the same size. On this occasion, density was reset to 80 plus minus 5 in-dividuals per jar･ This procedure was continued until they emerged to adults, but the density･per jar was reset to 40? 20 and 10 individuals with range of plus minus 5 in the third mstar,fourth lnstar and pupa, respectively. Water depth was 2cm throughout the experiment. Anamount of 0.1-0.3g per jar of finely grained mouse pellets (registered name NMF,manufactured by Oriental Yeast Co. Ltd.) was fed every other day. Water was not renewedduring each lnstar period unless it became turbid or rotten. This rearing method was adoptedto confirm the stage specific developmental period and the mortality under little stress fromhigh density and nutritive shortage, and to clarify the temperature dependent velocity of theimmature development.on the other hand, in experiment 2, the first instar larvae were placed in different in-itial densities ｡f 2n (n=3…8) per jar, and reared without the reset of density. Feedingschedu且e was the same as in experiment 1, but the rearing was conducted only under 25C･RESULTSExperiment I‡n jars at 28C? 13.8% of the first instar larvae moulted into the second instar between12 and 2逢hours after hatching, while at 25C and 22C, the second instar larvae were firstlyobserved 36 and 48 hours after hatching･ Frequency distribution of the timing that the first=Instar larvae successfully developed into the second instar under the three rearing tempera…tures was illustrated in Fig. la. The average periods of the first instar were 1.55 days at 28C,1.86 days at 25C; and 2.73 days at 22C. The mortalities during the period were 30.0%,7116.8% and 19.0%, at 28, 25 and 22C, respectively (Table.1)･Significant differences were found in the developmental period of the instar among thethree varieties, but no differences were detected on the mortality (P<0.05).In the successive instars, the average developmental periods in days prolonged as themstar advanced in each rearing temperature, and the frequency distributions of the period●flattened (Fig… Ib, c, d)･ The average periods in days of the second instar were 1.95 (28C),3･23 (25C) and 3･70 (22C)･ Those in the third and forth instars were 2.70 (28C), 3.62 (25C)4.09 (22C); and 4･51 (28C), 5.77 (25C), 6.25 (22C), respectively (Table 1). The differences ofperiods among three different rearing temperatures were significant (P<0.05) in all theseins亡ars･ No instar specific or temperature specific differences were found in the mortality(Table 1).The pupal period was the shortest among the immature stages, and less affected bytemperature examined. At all varieties of the rearing temperatures, the first group of adultsemerged by 24 hours after pupation (Fig. Id). The average pupal periods in days were ･29(28C), 1･49 (25C) and 1.(39 (22C) (Table 1)･ The differences in the developmental period werestill significant (P<0･喝. Mortality during the period弧ged from 9･S% to 19.7%.From these results linear regressions were expec…亡ed between the rearing temperature■(X) and the developmental velocity (the reciprocal of the average instar period in days) ineach instar and pupal stage (Yi...p). Equations were as follows:Yl-0.0456X-0.6456 (r2-o.9828, P<0.01)Y2-0.0406X-0･6506 (r2-o･8665, P〈O.05)Y3-0.0210X-0.2284 (r2-o.9252, P<0.05)Y4=0･0103X-0･0733 (r2-o.9044, P<0.05)Yl…4-0･0056X-0.0669 (r2-0.9392, P<0.01)YD-0･0293X-0.04…ア3 (r2-o.9880, P<0.01)Cal(:ulated developmental velocities in each instar at 3 temperatures were shown in Table IThe developmental zero of Cx. tritaeniorhynchus immatures estimated from these equationswas between ll and 15C･Experiment 2The density effect at 25C was summarized in Fig. 2 and Table 2. Overall develop-mental period in days was prolonged when the rearing density was increased. The prolon-=gation became more apparent with advance of the instar. It was within 0.ll days differencein the first instar (1.00 day in 16 and 64 individuals per jar and 1.ll days in 128 individuals),but nearly ten days in overall period (8･48 and 17.95 days in 8 and 256 individuals) (Table 2).Emergence of adult was observed synchronously in low densities but it became sluggish asthe density Increased (Fig･ 2)･ However, the first ecdysis to the next stage including the/emergence to adults was旨occurred nearly on the same day irrespective of rearing density･●except the highest density gr叩(256 individuals per jar) in which the emergence de二Iayed.Therefore the prolongation in the average period or the median of each instar should be at-tnbuted to the sluggish ecdysis to the next instar.72/�"-N宅諺^nS魯専尊台専慧烹ヨooo<-<Eコ雲量喜喜喜葺葺喜田[コ′ロ6′a左′Joい′　　ヽ�"sヽaCJ●壱　等　罵　申⊂コ●●□■コ[コ[コdt●ldIJロ告†q.i■勺1-t▼一l巳申140トヽOtha　^ヽlヽ占i　　…ヽヽ回J*---J--*'拍巾<s菖に'一光-ー一~s4､､ Ej ～s-l■,s_　､者'　E事罵　5　昏霞　壱　罵　等　罵言こ) ○＼It,○ロ　　トIISBrlc-jflォ■●1b寸c-T--o'do-----V_Y,●･~∠､ー.者==~㍍者　　　II::==■㍍㍍㍍㍍者　(f I-　-&-o■一　　　　い　　　　　ヽ□　rl者｣㍍㍍_･-■-　　　　ATI 51●[コ　手藁　葺　嘉　壱　専　罵　卓冒amxv川MI且(TON‥罵　罵　雪　害　罵　古事('｢ロ白き正た.:′-ヽJDヽ■㍍者l㍍者′hdlJ㍍㍍㍍者J∽白■Td+JwT■■ヽ′■sヽcdヽs者ノ■〔n4)B亡弓IsqJ白aBト㍍㍍者IBEd*+JsjqJl｣いej等CO　.者J-　Odd OL苗邑召I:己B�"�"-<　　en.s關頂童童l害通　-通㍍国通]･iHq)トーゴ･暫【i73===者⊂匂■J日h邑B一志琴nE割　軍票弐　買気語　呂葺望　E;冨転菅野　o o o o o o o o o　占o,占　に;占o<L>∈l･(刀4)ト,者l割j届!hO)Iコs匡<u｣一日=(U届巨4->Fj(Uコ=児)賀｢コmJ者■ーdt乃d)hローJ.Jく8日■萱ex⊂)h.tはU藏>T者者者者IS用召<usFLlo-芯>各-てコEj吋h占lLqhos●ヽ(刀者ヨ!rg□I, II..lT割'CqJOi-T者者者･･s(廿+JEjqJsPsls<D>｣qJbDodト者者者1d)><d･▼■,害.0C6H事L-(U削妄言書芸冨冨書芸書芸書芸約言書芸書芸書芸言岩書芸cof-52芸芸o∋　(一つ　ss所oo cyう　NCXI CO aう塗h.ij'言tj(⊃害B弘｢コ　rdぎ届=発割醒貞一SUI折ロo2:白o-a〔匂U;=IAqJMh･島fjqJ⊂】′-ヽUヽ_一′-ど基層A己Bト.I者LO抑d==者00　いD　いDUう　くD t､姐一　回KLK^Iss事事ss申割事ss申割事ss申　TF　'申⊂⊃　⊂>　o⊃⊂⊃　⊂>　⊂⊃T者者者者者1　1一者者1　T者者者者IlOO LO CMN O､I OqT者者者1  1者者者者者者者者者者者者者.･者　　s者-I寸　寸　ss申⊂⊃　⊂⊃　⊂⊃oo oo ooOO LO CMO〝　csj egCS]　CM Cい)00　くっ　いDCO　<^　-^T者者者者H LO T者者者者者者1o⊃　⊂⊃　⊂〕tD　⊂コ　い⊂〉T者者者,.者l　くD　-･イss所　LO　^T一⊂⊃　⊂コ　⊂⊃寸　^H　寸OO Lfう　OqCM C<1　<Nl乱　国u>WOT)　▼者一　eYうト一　寸　いDOqくコ　⊂⊃　⊂)oコ　⊂5　00y-}　o/つLiう　LO　�"ォ申丁者者者Sl⊂⊃　⊂⊃　⊂コc<i oq cxi咲)　LO CMN Oい)　Oい1ss申　s勺1　s寸sem&≠　き虎Ln s申　LL?I者■いo　^者<　CT>いD　くD tD▼者sLn　いD　くD亡ー　⊂⊃　亡一林▼･一　寸　†者■∫ l ,ロコ　⊂>　く丈0CJくXD LO CMCS]　CM COロ者　PH AH74The overall mortality was the lowest in 8 individuals group (28.1%). The rate increasedas the density increased, and the highest rate was observed in 256 individuals group (84.0/6)(Table 2). The age specific increase in the mortality was not distinguished (Fig. 2), and thedaily mortality was not different irrespective of density (2.8%, 2.5%, 2.2%, 2.2%, 2.4% and且･2% in 8, 16, 32,弛128 and 256 individuals per jar, respectively). Therefore, it wasstrongly suggested that the overall mortality was dependent on the overall larval period.su血prolongat血might be caused by the shortage of food in old instars of higherdensities through competition for food, because the number of pupae in 256 and 128 in-dividuals groups increased on the next day of the every other daily feeding. The averagenumber o壬pupae on the day of feeding was 2･86, while that on the next day was 4.43･Difference between two averages was statistically significant by paired t-test (P<0.005).DISCUSSIONThis experiment revealed again that the development of immature stages of Cx･tritaeniorhynchus follows the law of total effective temperature, and that the development wasstrongly affected by the larval density possibly through the availability of food amount perlarvae･ The immature period would actually differ by nearly 20 days according to prevailingtemperatures within the mosquito season in Japan, as the period calculated was 31.6 days at且8C or 12.4 days at 28C･ Furthermore, the period should change by the larval density, asascertained by experiment 2. Therefore, if the effect of the larval density is rational in theprevailing temperature, difference of another ten days, totaling 30 days, may be better totake Into account of the actual immature period in natural populations.AcKNOWLED GMENTSwe are indebted to Professor Yoshito Wada, Department of Medical Entomology, In-stitute ｡f甘ropical Medicine, Nagasaki University, for his valuable comments and critical/reading of the manuscript.75d叫250ユ･･150IIIKHIlト､屯I)'¥t: …,,,I ,,,.i Iitl･14･120ト%100hi;掛澗貞I'�"I1.*[I2GflllT｡丘l碧so.I4｡i…芸3｡I岳H愛201｡･,J:II＼,l0ノ}ぺ｣0a) 3-　■…~1----I-･ユ--rr= t3----4…‥ ~■P"�"　-　-　-AcrauAヽ　　　　^--" '-一-/i:　　ー-X-くl,., l,一■　…l……　………■,■.-■i?ll…■仲)/^-N/′-ノ　_一一-I^-xf¥V ,ヽ,＼≡≡:e≦eゝ.…ゝ丁…I占･5t/4030201･135SIL52015111一10o＼ /へノ＼I　　　　＼＼＼√′一■　＼l′′I^**＼_I ､0　ヱ　4　占　H 10 lヱ14 16 1且　王0　丑　24　26DAYS AFTER HATCHINGfI.:t･,.HiI':I.H･.白] …Jkm. ,%I;! A｢ヽIII∫ll l%′′(d)＼㌔/′vx,㌔(e)■-　…■ll～lJl5F I卜,,Iリ03530＼＼%　　′1(0′　-　■-■:=iド∫II九Il25 Iサ' ,･5nt J･ /I!/;i I,,llII∫II′､l,　　　′I Il爪l, IIttlりl･lr>0　ユ　4　6　8 10 12 14 IdFigure 2･ Developmental period in days of immatures reared in different densities ranging from 8 to256 per jar at 2i5℃. (a), 256; (b), 128; (c), 64; (d), 32; (e), 16;軌乱76ous_nOい]sトJ∈匂ゎ･島cqJ'てコsトJ良也)ト者者者lくじ1ヰ｣莞-18国gE罪q)ヒ≡〔乃q)ト者者者l盟E!聖EdE:島い=o)h義一弓t!〔)g-守詔CO>*o87日sj■ :=≡yJロ∈,TQJ払"73s林者-蔓色,日払(a｢===屯)>q)-8i鳶色)･与Jo弓▼者者■一口弓UU<dGle相性)r==毒,凸鵡童=与ト帆jヨ田'て,良--'てコoA I-Iト者者者l也)a7-7,･S亡8sJ者Jsj也)E事弘o<D>屯0I-⊂】I亡づち百コUU<d葛　宗試写告品等葛　E=巴害占oおoお邑　害ヨ臣E=巴県:<2　t一虫害岳ふ性(ddl荒性;志等LOCO<>Jr-(s■Jせヨ^^トいD机rてコhmTO臼eい]ss申　OYう　L者n　ロ⊃　t一者者1　00o5　00　T者者者1 ⊂⊃　00　O=⊂ロ　ト-　L者f?　廿　Oい]　Now一)　OY一)ーl　⊂⊃　⊂∋　Ln∈⊃　LO　<NI LO ICs廿　OYう　CM　<N( .-I r-島　芸コ芸苫芸誓i-1　_: _; ▼｣　J sJ め塗臥芸亡81J者.Ji,.1o冒IbDト≡1q)己q)COsis.)s者者者者者者者lコTdEdい=o,(コ:石蓮o�"43用･B払qJ出｣'訪日名13:isj==芦oO　-3者I ey一)　く=>　OO COくJ〕　ロ〇　T5者-I LO CO　者-1eつ　廿　m tt者s者者-　sす1*　GO(:l⊃　い.0 UO Ol一>　OY一) Oい]oい]　∈∋　T-■　⊂⊃　sS申　m(:亡l　⊂h　∈n OX⊃　00　CXIcM Csl C*う　^F　寸　s所いD OO　^　Cい]　いD　∝)Lf者)　N　いD CO T者者<CM i一一qJb山一8+Jt乃slJ開Uロq),エコJ者-o,+JT者C,u,工]Uく匂Q)3者_l∽4)林sコJ_ioda=置I-･者s【弓2wo昏⊂∋Ln良fc<L>己*4_)<L>,弓sl者sJosトJ.⊂]U者l者I■F弓r-Bsト■百oト㍍者SL<4-I(刀県､【コ*77REFERENCES1) Mogi, M･ (197恥Pop¶[lation studies ｡n mosquitoes in the rice field area of N喝asaki, Japan, espe-cially on Culex tri由eniorhynchus. Trop Med., 20, 173-263.2) Nakamura, H. (1978): Oviposition preference of Culex φφtens molestus and C. tritaeniorhynchus sum-morosus onto the waterモ3 conditioned by the egg rafts or the larvae. Jpn. J. Sanit. ZooL, 29, 117-123.(in Japanese with Engli血summary)3) Nakamura, H… (1979〕: Experimental studies on the crowding effects in the larvae of Culextntaeniorhynchus summorosus, C. φiφtens φaliens, and C. φφtens mokstus･ Jpn. J. Ecol., 29, 163- 170･(in Japanese with Eng】ish synopsis)4) Siddiqui, T.F･, Aslam, Y. and Reisen, W.K･ (1976): The effects ｡f larval density on selected imma-ture and adult attributes in Culex tri由eniorhynchus Giles･ Trop. Med., 18, 195-202.5) Takagi, M., Sugiyama, A. and Maruyama, K. (1995): Effect of rice culturing practices on seasonaloccurrence of Culex tritaeniorhynchus (Diptera: Culicidae) immatures in three different types ofnee-growing areas in central Japan･ J･ Med. Entomol., 32, 112-118･6) Wada, Y･ and Omori, N･ (1971): Ecology of vector mosquitoes of Japanese encephalitis, especially ofCulex tritaeniorhynchus summorosus. 4. Development of immature stages of Culex tritaeniorhynchussummorosus with particular reference to temperature in spring and autumn. Trop. Med., 13,193-199,7 Yos血ida, M, Nakamura, H･ and lto, S･ (1974): Effects of temperature and photoperiod on the larvaldevelopment in Culex tritaeniorhynchus summorosus Dyar. Jpn. J･ Sanit･ Zool., 25, 7… 11… (in Japanesewith English summary)

A Laboratory Experiment on the Larval Development of Culex tritaeniorhynchus (Diptera: Culicidae) Giles under Different Temperatures and Densities

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A Laboratory Experiment on the Larval Development of Culex tritaeniorhynchus (Diptera: Culicidae) Giles under Different Temperatures and Densities

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