JapaneseJapaneseSociety Society ofAppliedof Applied Entomology and Zoology
Appl. Ent. Zool, 21 (2): 191-202 (1986)
Adult Responses to Larval Rearing Density in Mythimna sEzparata
and Mythimna pallens (Lepidoptera : Noctuidae)i
M. G. HsLL2 and Kazuo HiRA[
71]hoku jVatienat Agriculturat EKt)eriment Station
ildbrioka 020-01, .laPan
(Received April 16, ]985)
Larvat rearing density iiad ne effect upon ad ult I'emale flight activity in ilij'th imna soparata, M. separata females subjected to the duat stresses of c/ro"'ded larval reating comditions and
Hight over a 24 hour pericd, iaid t'cwer eggs than l'en]a]es from so]itary rearing conditions. changes, :If, patlens females showect no such fecLmdity There was a positive linear relationship between pLLpa] weight and fecundity which
diffl]red according to larval rearing density ancl flight treatments in both spccics, The
difl'erences are interpreted as allowing ('cmales to maintain relativcly normal levcls of l'ecun-
dity fo11owing stresses (particularly weight reduction) associated wit}i crowded Iarval rearing and prolonged Hight, It is concluded that crosvded larval rearing densities do not stiTnLilate
flight activity, and that both species may be cqually capable ofsustained flight.
INTRODUCTION
The oriental armyworm, iT･lythimna (=I'seudketetia) soparata WALKER is a scrious pcst of grain crops and pasture in Asia and Australasia (SHARMA and DAviEs, 1983), Studies carried out in China (Li et al., 1964, 1965; LiN and CIHANG, 1964) and Japan (HiRAi, 1982; OKtJ, 1983) demonstrated that this spccies is a strong and rcgular migrant, shifting its latitudinal rangc annually in association with clirnatic fluctuations and prevailing winds (UMEyA et al., l983; ZHAo, l983). `armywormi-type [`phase As in other species, iV. soparata Iarvae undergo variation'' dependent upon la-'al rearing clensity. Compared with larvae rearecl in isolation, those
larvae rcared in crowded conditions are melanised, develop more rapidly, eat more food, arc mDre active, give rise to smaller pupae and are rnore tolerant ofless palatable food and starvation (IwAo, 1962, l963, 1967 a, b), He also showed that rearing density does not aH'ect fecundity, thc timing of oviposition, or adult colouration ;, but that aclults
fi]om crowded rearing conditions live longer and have a lower water content, It has been suggested that phase variation may afl'ect adult behaviour and physi-
t This rcsearch f'orins part of tt]e studics on ciev{:Loping f'orccastiiig techniques of migrant insect pests (l983-1987) pro.iected by the )vlinistry of Agriculture, Forestry, and Fisheries, Japan. Part of t}us paper wag rcad at the annual meeting of' the Japanese Soeiety of Applied Entomo]ogy and Zoology (LJtsunomiya, April, I9B4>, 2 Present addrcss: Entomolog.;/ Dit./ision, DSIR, l'rivate Ba.u, Auckland, A'eiv Zeatand
191
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192 M. G, HiLL and K. HmAi
elogy in such a way that adults emerging from crowded larval rearing conditions are likelyto be migratory rpore compared with similar adults from solitary rearing condi- tions (IwAo 1962; GRuys, 1970), Little work has been conductcd on this aspect, although some rccent work with the Afi'ican Arm}rworm (Jipedoptera exempta (WALKER)) suggegts that larvalrearing densities do aflbct aclult flight activity (PARKER and GATE- HousE, 1985 a). The work was designed to . present test the eflects of M, soparata larval rearing den- sity upon adult flight activity and fecundity. A second closely relatcd species, M. was also tested. Itdifllers !14. ?allens, from soparata in being non-migratory, slow develop- ing and does not show Iarval phase variation. Thus, a comparison between thc two species islikelyto shed light onto thc significance of phase variation.
MATERIALS AND METHODS
1) I}tsectrearing. M. iV. soparata and paUens were rcared by identical methods, using an artificial diet (HiRAi and SANTA, 1983) and orchard grass (Dactyiisglomerata). Larvae were reared in groups up to the 2nd or 3rd instar, Subsequcntly, those to be reared singly "'cre placed alone in petri dishes (8.5 cm diam. × 2 cm depth). Larvac rcared in crowded conditions were held in groups ef ca. 50-200 in plastic lunchboxes (27,5 cm × 19 cm × 6.5 cm). On reaching thc final instar, thcse crowded Iarvae were scored for body colouration using a five point scale (1=pale, 5=black (IwAo, 1962s OGuRA, J975)), and placed in groups of five in petri dishes. All five larvac within a the same petri dish had colour score (M, pallens does not clisplay phase variation or colour changes in response to rearing conditions). Larvae were rearcd at 250C, 50-6091. RH and 16L-8D regime. Cultures were ex- amined daily and newly formed pupae were removed and weighed. Pupae were stored fbr six days under the same conditions as those for larval rearing, and then transferred to a constant temperature room at 200C, 60-80?,S RH and 12L-12D reverse Iight regime, Adult moths were weighed when 12-24 hr old, to allow the determination ef the relation- ship between pupal wcight and adult weight, Emerging femalc moths svere marked fbrindividual idcntification with a feIt marker (BRussARD, 1971). 2) Flight behae/iour. Flight behaviour was measured using a flight balance designed by GATEHousE and HAcKETT (1980) and also by using a simple sinoked drum kymograph similar to that used by HwANG and How (1966) and MAcAuLAy (1974). Both flight apparatuses were operated at 20CC with a reverse 12L-12D light regime ancl 60-80% RH. The flight balance is unique in that it allows a tethered moth to walk on a revolv-
ing drum or fly in a stream of air at will, The airflow through the apparatus was l.54 m.s-1. The kymograph consisted ofa smoked drum rcvolving once per day. A piece of soft iron wire, 30 cm long, was suspended horizonta]ly and clampcd at one end, The free end was bought into contact with the edge ofthe clrum, and a moth was suspended
about 8 cm away firom the fi'ee end of the wire. FIight activity of the moth caused the end of the wirc to move in a vcrtical plane and this was recordecl on the smoked drum. Preliminary observation showed that moths can livc fbr several days without food, but that activity was greatest within the first 24 hr ofattachment, Obscrvations on both ild', separata (HiRAi, 1984) and S. exempta (RosE and DEwHuRsT, i979; GATEHousE and HAcKETT, 1980) suggest that adult armyworm migration occurs befbre ovary maturation
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Adult Responses in Armyworm 193
60 o
245oO
DAYNIGHT
. 123456789 tO ll 12 FLOWN EMEHGE HOURS IN SCOTOPHASE
Fig. 1. Periods of emergence and fiight for Fig. 2. FIight balance data: M, soparata. Per- female rnoths used in fiight behavieur tests. centage of moths 1) taking off on their first flight (open circles), and 2) taking eff on any flight (solid circles), within each hour of the
scotophase, n==40.
and probably begins on the first night fbllowing eclosion (see also OKu and KoBAyAsHi, 1978;JoHNsoN, l969). Accordingly, it was decided to test al] moths on both apparatuses ever a 24 hr period, starting in the first two hours ef the photophase (the scheme employ- ed is illustrated in Fig. 1). Fernale moths were used which emerged during the 12 hr period beginning 2 hr into the previous photophase. Thus, at the tirne ofmounting on the apparatuses, all moths were l2-24 hr old and had experienced one scotophase period. They were not fed before the test. Both M. soparata and M. Pallens were tested on the kymograph, only M, soparata was tested on the fiight balance. 3) Fleezandity, After removal frem the kymograph, females were placed in mating cages along with the not-flown females and males, and supplied with 1O% honey solution ad libitum. Mating occurs primarily during the second half of the scotophase (HiRAi and SANTA, 1983) and cages were checked hourly between hours 6 and 10 ofthe scoto- phase. Mating pairs were removed and held in 1l cm diameter × 7 cm deep plastic cages with vented lids. After copulation, the male was removed, the female was identified by her markings and supplied with 10% honey solution and folded waxed paper fbr oviposition, The paper was changed daily until the female died. The females were dissected and the remaining mature eggs counted. Those females having few (<20) mature eggs were considered to have laid their fu11 potential of eggs. Five females with greater numbers of mature eggs were considered to have died prematurely and were excluded from the analysis. Data on fecundity, pre-eviposition and oviposition periQds were colrected from fe- `not `flown' males flown' as well as from those on the kymogtaph for both solitary and
crowded rearing conditions.
RESULTS
M. soparata iarvae from solitary rearing conditions were pale, and predominantly in colour categories 1 and 2, with a few in category 3. Those from crowded rearing con- ditions were dark, mainly from colour categories 4 and 5, with a few from 3. Female pupae frern crowded rearing conditions weighed less than those from solitary conditions (Table 1). Pupae of both species suflt]red equivalent weight reductions. There was no significant diflbrence in weight between larval colour categories within
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l9 Table 1. Pupal weights offernale Al. soparata and M. Paltens Solitary Crowded Larval colour category 1 2 3 s 4 5 M. soparata .257.O12 Mean weight (g) .309.O15 ,319 .328028 .277,024 .272,O18 95% C.I. .O18 . 37 n 36 27.315,O1472 9 10 22,265.O0969 Combined rnean weight {g) 95% C.I. n % weight reductien 15.9% M. pallens Mean weight (g) .327.Oll37 .276.O1337 95% C.I. n % weight reduction 15,7%, C,I.±confidenceinterval, rearing densities for M. soparata (Table 1) and no diflerences were detected between these colour categories in the ensuing analysis. There was a strong relationship between weight of I day old pupae and adults 12-24hr old (adult weight (ptg)=O.54 pupal -68,3, weight (ptg) r2 == .74; P<,OOI). Night balance data (M. soparata) No moths fiew during thephotophase, Both estimates offlightperiodicity ofactiv- firsthour of ity (Fig. 2) show similar features, namely a peak of activity during the darkness, fo11owed by a decline, and a second peak in the second half of the scotophase at about hour 9, The distribution of fiight time was skewed (Fig. 3) with most moths fiying for a short time and a few fiying for a long time. One moth (from crowded rearing condi- tions) flew fbr all but 8 min ofthe twelve hour scotophase period. There are no diffbr- ences between crowded and solitary reared moths, either in overall time spent flying or pattern of activity (Fig. 3); and there is no relatienship between pupal weight and fii.crht time. Eight ofthe moths (17.8%) fiew for >2 hr, which is the length oftime sug- gested as a demarkation between potentially migratory and non-migratory individuals in S, exempta (PARKER and GATEHousE, 1985 a), KTmograph data (M. saparata and M. paglens) The kymograph records have been analysed by dividing the 24 hr period of flight for each moth into three 3-hr periods in the photophase, and four 3-hr periods in the scotophase. The activity during the first 8-hr period of the photophase has net been analysed because the moths were attached to the kymograph wire during this period and the amount of observation time available is variable. The mean time spent fiying during each of the remaining seven 3-hr periods is shown in Fig, 4 fbr both species. Crowded reared females Qf both species flew fbr signifi- cantly less time than solitary reared females (Fig. 4;F=4,5, 1,8e d.f,P<,05), and there was no diflhrence between M. soparata and M. PatZens in total flight time (F--3.5, 1,80 NII-Electronic Library Service JapaneseJapaneseSociety Society ofAppliedof Applied Entomology and Zoology Adult Responses in Armyworm 195 25 20 15 to eilLFz-ith-EFFz-oorwa s o s-6 S-9 g-2 o-3 3-6 6-9 9-12 -LIGHTPHASE-# - DARKPHASE- 2S 80 !e 70e 6oFo 15 50ES 40<- rio 30oN 2o 5 10 m o e -30 .60 .90.nml-12e 120- 3-6 6-9 g-12･ O-3 3-6 s-9 9-t2 -LIGHTPHASE- - FLIGHT TIMESCMINUTES> DARKPHASE. Fig, 8, Flight balance: M. separata. Fig. 4, Kymograph data, Percent time spent fiying dur- Distributions of flight times for ing seven 3-hr periods throughout the day. Bars are 95% solitary (solid, n==2l) and crowded cenfidence intervals. C= crowded r ¢ ared; S=solitary reared. (open, n==24) reared larvae, d.f,p>.05) on the kymograph. The data for M. soparata show no difference in flight activity between the seven 3-hr periods (square root transformation, F==1.8., 6,532 £ while the show a significant activity d. , P>.05), data for M. Pallens declinein flight with time 6,280 d.£ and hence they were rnore active during the (F=:7.0, , P<.OOI), photophase. This suggests･that in both species, the lack oftarsal contact on the kymo- graph disturbed the moth's natural nocturnal activity pattern, Plecundity Fecundity data for each species are summarised in Tables 2 and 3. In M. separata, there was no significant diflbrence between flown and not-flown or solitary and crowded rearing treatments. However, there was a significant interaction between treatments, showing that rnoths subjected to the dual stresses of crowded larval development and flight laid fewer eggs than solitary reared not-flown moths (1,164± 255 vs. 1,509± 124, P<.05). In addition, solitary reared flown moths have a shorter oviposition period than moths in the other categories (7.0± O.8 days cfl 8.4± O.3 days, p<.025), while NII-Electronic Library Service Japanese SooietySociety of AppliedApplied Entomology and Zoology 196 M ．G ．｝｛1 正 正 and K ． HiRAr 「 「 @ L で o δ q O o 頃 ． O ． 鱈 剛． O ． O ． O ． 頃毛 で 一 O 【 一 。喟 ◎ O 刷（ ま ［ ［ 刷冒°・ 醜 邸 ≧ の 霧 O 詮 甥 餌 で 6 回） δ ， D “ 〇 〉 一 一 承 卜 門 ． ． iR ． ， 鮒 ． ， ○◎ o っ ○ o つ Qo co の嘱で聾g i ≧ 口 δ う ． Q uR广 O 刳． σ◎ 頃 り っ 寸 O 州 cQ o ． ． ． ← 承 寸 ． 寸 ． 寸 。 ． δ O O OO 嘱の（ O OO O O 醜 Q【 司 O 艮 場 鵲 咽亀 承 ＞ ）砦 匿 OI 鵲 O 崘 【 o ⊃ Oa ⇔ う 」 ， 寸 ． ． 聡 ． ． ． ， ． Φ の 』 寸 申 寸 嶋 餌 遷 ） δ の 圃口 6O ｿ う ， o ⊃． O 一 一 艮 承 ． ． ． ． 。 ． 劇「 唱 O ○◎ ゆ の 甥 a ト 刷 ＞ 帽 署 。 鵠 一 窃 晋 。 の 郁う − 。目 日 bobQU ＞ 出 刷 q 寸 o う N 自 習 αう O O っ ， ． ■ ． ， ． ． O （ 唱 k 帽 話 嶋 寸 QQ o◎ 頃 守 O め − 辞 の 頃 寸 寸 欧 僅 巷 壱 HO α ． 卜 寸 訓 廖 O ． ． 禽 寸 αう O う 价 ． ． ． ． う Q っ で 絹 求 り 長 誤 O り 卜 曇 界 ＝ 貯 寸 ト 卜 竃 8 @ 睾 窯 で 鵲 り 些 頃 aRO 畿 的 ． ． ゆ 嶋 洗 O N 卜 1 ODQ 斜 ． ． u。 曇 ． ， ， ． 鵜 一 Oo 個 丶§ 唱 ，R ◎ 寸 O 寸 屓 ［ ◎ 寸 、 国 の o う °D ト 卜 Qo 蝉 頃 寸 寸 ℃喟 ミ・ 經 ミ ． 紡 ． α o っ 啓う ［ b N 個 ° 「 ま 囲 N 麟 。 。 国 室 照 卜 踏 @ @ 窯 呂 【 一 卜 の ， 頃 ． ． 』 O O ． ， ． 蔚 ． Qou 創 守 の め OoD N ○○ （ 艮 掣う り 艮癢 ＝ ま 臼 齠 【 ） 窘 2 8 遇 。 8 臼 a9 頃 ． 。 O O O O 鄭 う °。 ． ． ． ． 隣 ■ と ， ぷ り 【． 逡 一 Q◎ ［ O ． 臨 o う 8 螂 う °っ 一 創 ． 軌 ． 邸 oQ 邸 0 一 一 〉 〉 』 』 ←ω 一〇 q 霞 哨 咽 O 8 り ． 唱 ¢ で で 口 【 O ． ≧ ω o 爵 り 卜 O 唱 喝 ℃ ℃ 唱 ⊃° ≧ 醤 嵎 ≧ ≧ § 蟷 O 口 ［薯 O ［哨 口 寸 ぴ 」 で 巳 。 』 。 OQ ． う O の 811HO O °。 O °。 冂 hO 口 冐 ≧ 津 o o 【 唱 尉 口 中 憾 ． ≧ 【 ぢ o ぢ 乞 田 宕 卩． 。 NII-Electronic鮎 ⇔ D 羣 。 卜 ゐ 儒 已 ヨ霧 1 Library§ 邸 で 禽 で 塁 駐 ミService建唱 蟄 ． ミ． JapaneseJapaneseSociety Society ofAppliedEntomologyof Applied Entomology andZoologyand Zoology Adult Responses in Armyworm 197 Table4, M. soparata regression analysis of fecundity versus pupal weight int?sgePt s,D.*.Slope S.D.b r2 n (b) p<,OOI<.OOI Flown Crowded -395-1,334276273 6,2427,987 1,085 IO20 Solitary 781O.81O,85 Net flownCrowded 659404 316371 2,4643,432 1,1oo1,140O.15O,26 <.05<.Ol 2928 Solitary *S.D. ==standard deviation, Table 5.M. PaUens regression analysis of fecundity versus pupal weight Intercept SIObP)eS.D.b S.D.*. r2 p n (a) Flown Crowded -406 4763co2642934,3632,290 1,635 O.37O.S3 <.05<,05 14l3 Solitary 217 992 6 045 927853 O.69O.28 <,OOI Not flownCrowded '1970 21 <,05 15 Solitary-772 307 7 *S.D.=standarddeviation, tooo ISOO 1500 // l5g8L 'La - looos:L loae - S : MEANtS.D. S:MEAN ± S,D. - .D. seo/ C:MEAN:S.D, soo ,2s ,So ,35 .4e ,IS ao ,2s ut .3s .40 PUPAL WEIGHTtGRAMMES1 PUPAL WEIGHT lGRAMMES) Fig, 5. ML soparata-regressions of pupal weight Fig. 6. M. pailens-regressions of pupal and fecundity. C== crowded rearing, S::=solitarily rear- weight and fecundity, C=crowded rearing, ing. Solidline=mothsflown,dashedline==mothsnot S:==solitarily rearing, Solid line=moths flown. fiown, dashed line ==moths not flown, flown moths lay a higher percentage of their tetal egg production during the first three days, compared with not-flown moths (66.1%±4,1 % c £ 57.7% ± 4.1 %, P<,Ol). In M. Pallens, there is no difltirence in fecundity between treatments. However, NII-Electronic Library Service JapaneseJapaneseSociety Society ofAppliedof Applied Entomology and Zoology 198 M, G. Hu.i. and K. HrRAr flown moths have a sherter oviposition periocl than not-fiown moths by one day (8,1± .7 days ci 9.1 ± ,7 days, P<.05) ancl lay a higher percentage oftheir total egg productien during the first three days (54.6%± 6.2% cfi 48.4% ±4.8%P demonstrated between duration of moth flight and fecundity nor any significant increase in explained variance by adding fiight time as a second independent variable to the pupal weight-fecundity regressions. DISCUSSION The activity pattern recorded with the flight balance, showing a peak of flight after dusk fo11owed by a second, smaller peak in the latter part of the scotophase, is broadly in agreement with data collected for S. exempta, using a similar machine (PARKER and GATEHousE, 1985 a) and by field observation (RosE and DEwHuRsT, 1979). Flight activity peaks after dusk have been recorded fbr many species of Lepidoptera using traps (LEwis and TAyLoR, 1964), radar (LiNGREN and WoLFF, 1982) and actographs (HoLLo- wAy and SMiTH, 1975; LEppLA et al,, 1979). The skewness of the distribution of flight duratien suggests that individual moths within the population exhibit diflbrent propensities for flight, A highly skewed distri- bution offiight activity appears to be a common feature fbr most insects tested (JoHNsoN, 1976; PARKER and GATEHousE, 1985 a; HARRisoN, 1980), suggesting that polymorphisms of either morphological physiological or behavioural characters are a common feature in flying insects. The difurence in diurnal behaviour obtained on the fiight balance and , patterns 'the kymograph is striking. The fact that the kymograph destroys nocturnai behaviour pattern of the moths suggests that those apparatuses designed for nieasuring flight without providing tarsal contact (e.g. CHAMBERs et al., 1976; HwANa and How, 1966; NAyAR and VAN HANDEL, 1971; RowLEy et al., 1968) may seriously d'isrupt flight behaviour, and be unsuitable for measuring fiight activity. An important diflerence between the two types of apparatus is that those denying tarsal contact will measure ability to fiy while those allowing the moth te rest and walk between fiight will measure willin.ffness to fly. Rearing densities The results from the fiight balance does not support the hypothesis that crowded NII-Electronic Library Service JapaneseJapaneseSociety Society ofAppliedof Applied Entomology and Zoology ,'Xdult Responses in .dtrmywerm I99 reared armyworm are rnore likely to be migratory (IwAo, 1962s GRuys, 1970) or more active (HiRATA, 1956) than solitary reared moths. Studies ofmigrations ofi14. soparata have also suggcstcd that phase change associated with Iarval rearing density is not an important factor in the migration of adults (OKu, J983; OKu and KoBAyAsHi, 1974, 1978). However, thcse findings difller I'rom thosc of PARKER and GATEHotTsE (1985 a) ``migratoryT' who found a higher proportion of' types in crowded cultures of S. exempta, Oviposition and.fZicundi4J, The observations that the pre-oviposition period is not aff'ected either by larval rear- in.cr density or fiight and starvation and that total fecundit)t' is not affected by larval rearing density support the findings of HiRAi (1984) and MiyAHARA (1978) that ovary maturation is closely Iinked to adult nutrition. In centrast, S, exempta adults require only water for ovary rnaturation, and fecundity is more closely linked to larval nutrition (GuNN and GATEHousE, l985), Fecundity of ildr. seParata is only signilicantly depressed when subjected to the dual stress oflarval crowding and adult flight. HiNToN (1981.] lists 1 1 previous studies in which larval rearing density has been shown to afllrct fecundity in Lepidoptera. Papal weight=jFbcundit.7 retationship The strong relationship bctwcen pupal or adult weight and fecundity in this and other studies (GRuys, l970; HiN'roN, ]981; RoTHscHiLD, I969; W.xLoFi; et al,, 1948) su.cr.gests that the eflkcts of larval rearing density and adult flight activity treatmcnts should be interpretcd according to their eff'ects upon this relationship (Figs, 5 and 6) rathcr than thcir eflt}cts upon fecundity alone (Tables 2 and 3), For iif. soparata, there arc ]arge difll rences in the weight-fecundity relationship between treatments CFig, 5). This may be best il]ustrated by comparing the predicted fecundities fi'om the dashed and solid lincs in Fig. 5 fhr rnoths ofmean wcight from each of the larval rearing densities. Moths fi'om solitary rearing conditions sufller a 209h reduction in fecunclity (ranging from reductions of40?,S to 7C],･t at 1 standard deviation on either side ofthe mean) as a result ofbeing flown and starved for one day, while those from crowded rearing conditions sufi'er a 49,S- reduction in fecundity (ranging fi'om a rcduction of 16% to an increase of69i at 1 standard deviation on either sidc). Further- rnore, comparing thc solid lincs in Fig. 5, it is evident that the response of fecundity to pupal wcight diM:rs strongly between the solitary-reared and flown and crowded- reared and flown treatments. Because the response line fbr crowded-reared and fiown moths has been shifted to the left re]ative to the solitary-reared and flown moths, the moths from crowded larval rearing conditions are able to maintain normal fecundity levels (relative to solitary-rcared and flown moths) foIlowing sustained activity, in spite ofweight reductions, This response may be associated with larval phase change. Differences in the il4. pallens weight-fecundity rclationship between the various treatments are not so distinct as those for .･V. sttt)arata (Fig. 6). In contrast to iVI. separata, the regression lincs predict little or no loss in fecundity in response to flying in either crowded or so]itary rearing categories. This cou]d be linked to the presence oflarval phase-variation in iV. soparata and its absence in M, PaUens, Two other examples were ibund of significantly diflbrent responses of fecundity to weight change. These are liphestia elutella Ht',BNER reacting to diflferences in rearing conditions (WALoFF et al., 1948) and Bapakts Pinniarius L. reacting to larval rearing NII-Electronic Library Service JapaneseJapaneseSociety Society ofAppliedof Applied Entomology and Zoology 2eo M. G. HiLL and K, HiRAi density (GRuys, 1970). Neitherspeciesundergoes phasechange, Whire the physiologi- cal mechanisms leading to these diflbrent responses are unknown, they may have the function of reducing or eliminating fecundity losses in response to weight reductions caused by crowded rearing conditions, However, a fuIl explanation of the results in Figs. 5 and 6 must await the outcome of further research into adult physiology. Dij7lerences between M. soparata and M. PaUens A significant diflercnce between M. ,roparata and M. Pattens is in their larval develop- ment rates. At 25eC, the larval period of M, soparata is about 18 days (HiRAr and SANTA, l983) and of M, paltens, 50-60 days (HiRAi, unpublishecl), while theiv final pupal weights are similar (Table 1), M. pallens also has a lewer fecundity than M. seParata (Tables 2 and 3) and is adapted to a sedentary lifestyle, being bivoltine in northern Japan (OKu, I981), and having a winter diapause. M. paUens appears to be less susceptible to fecundity changes in response to fiying and rearing conditions compared with M. sopa- rata (compare Tables 2 and 3, Figs. 5 and 6). This teads to the hypothesis that long larval periods may, fbr reasons unknown, confer physiological robustness upon Tesulting adults, and is supported by the observation that in the absence ofintra-specific competi- tion, solitary reared M. saparata dcv¢ lop more slowly than those from crowded conditions (IwAo, 1962). In addition, it suggests that M. seParata may not be physiologically more capable ofdispersal or sustained flight than ild'. Patlens, Recent work with S, exempta has shown that flight activity is controlied mainly gcnet- ically and secondarily as a response to rearing density (PARKER and GATEHousE, l985 b). Migratory flight is seen as a method of exploiting new growing areas during the rainy season and polymorphism for flight is retained within the populatien by continual changes in selective advantage between sedentary and migratory types between the seasons. This is a highly plausible model which may prove to be appropriate for describing M. soparata migration, in spite of diflerenccs in ovipositional physiology between ilct. saparata and S, exempta. However, the results presented here show that crowded rearing and phase change in iV. soparata does not enhance flight activity. They suggest that migration and sudclen outbreak ofM, saparata need not originate from previous eutbreak populations, and that factors initiating migratory flight may therefore be related to factors other than Iarval rearing conditions, ACKNOWI.EDGEMENTS MGH wishes to thank the Science and Technology Agency ofJapan for providing financial support in 1983 (Japanese Government Research Awards fbr Foreign Specialists), and Mr. Y. MiyAHARA, Hcad of Entomology Lab 1, Tohoku National Agricultural Expcriment Station, tbr providing facil{Lies, Mrs. I(eiko KoNisHi provided technical assistance, and Tony CoopER, Applied Mathematics Division, DSIR, Ncw Zealand for statistical assistance. 1)rs. A. G, GATEHousli, T. OKu, P, SiNGH andJ. CI,EARwATb/R providcd valuable comments on earlier drafrs of the manuscript. REFERENCES "ubiquitous" BRussARD, P. F. (1971) Field techniques t'or investigations of population structure in a butterfiy. J. Lep. Sbc. 25:22-29. CHAMBERs, D. L.,J. L. SHARp and T. R. 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T, CHANG (1964) Studies on thc regularities of the outbr'eak of the oriental armyyv'orm (Leuoania soparata WALKER) V, A modcHbr seasona] long-distance rnigration of the oriental army- worm, Acta Entomot. Sinica 3: 93-IOO. LTNc}REN, P. D. and W. NN'. "'oLFF (1982) Nocturnal activity ofthe tobacco budworm and other insects. In Biemeteorolqge' irt IPM (J, L, HATFiELD and I,J. THoMAsoN, eds.) Academic Press, New York, pp,21l- 228. NII-Electronic Library Service JapaneseJapaneseSociety Society ofAppliedEntomologyof Applied Entomology and Zoology 202 )L･I, G, HTT,L and K, HmAi MAcAuLAy. E. D. M, (1974) Lipid storage in the pre-imago and young adult I'lusia gamma. EntomoL tlxp. Appt. 17: 53-60. )vllyAHARA, Y. (l978) Efllrct ofthe intakc ot'sttgar at adtLlt stagc on thc tnating ol' Leucania soparata and ilgrotis ipsilon. Proc. Assoc. 1'lant I'rot. Kyushu 24: 101-104 (in Japanese>. NAy,tR, J, K. and E. VAN HANDEL (19711} Flight performanee and metabolism of the moth spodoptera JYngiperdla, .L insect, Ph.ysiol, 17: 2475-2479. OGiJRA, N. (1975> Hormonal control oflarval coloration in the urrnyworm, Leucania soparata. J. Insect. Piij's'iol. 21: 559-576, OKu, T. (1981) Notes on some grass feeding noctuids ef the genus :VI'thimna in Tohoku district. Ann. Rep. Plant Prot. Aiorth Jopan 32: 42-43 CinJapanese). infestation Lhe OKLr･, [[L (1983) Annual and Geegraphical distribution ot' crep in Northern Japan by oriental arrnyworm in special relatien to migration phenomena. Afisc. Publ. Tbhoku :Vatt, Agric. Eep. -49 Stn. 3: 1 (in Japanese). OKu, T. and T, KoBAyAsm C1974} Early summer outbreaks of'the orientai armyworm, iva'thimna separata WALKER in the [I'ohoku district and possibtc causative t'actors. APPI. Ent, 2bol. 9: 238-246. OKu, T. and T. KoBAyAsHi (l978) Migratory behaviours and lil'e cycle of noctuid moths (Insecta: Lepidoptera) with notes on reccntstatus oS'migrant spccics in northern.Japan, Butl. 7'ohoku A･'gt. A,gric. Exp. Sta. 58: 97-209 (in Japanesc), PARKER, W, E, and A, G. GATEHousE (1985 a) The eflbcts of Larval rearing conditions en flight per- i'ormancein females efthe African armyworm, 5Pedoptera exempta (WALKER) (Lcpidoptera: Noctuidae}. Bull, Entomol, Res, 75: 35-48, PARKER, W. E. and A. G. GAT-ioitsE C1985 b) Gcnctic factors controlling []ight performance in the African armyworm moth, Sbodo.btera exemPta (WALKER) (Lepidoptera: NocLuidae), Bult, E}ztomol, Res, 75: 49-63, RosE, D. J. W. and CJ. F. DEwHvRsT (1979) The Afi'ican armyworm, EPodytera exenipta-Cangregation of rnoths in trees before flight. Ehtomol. IlxP. APPI. 26: 346-348. RoTHscHiLD, G. H. L. (1969) Observations on the armyworm, SPodaPtera mnuritia acroip,ctoide,s GN. (Lepi- doptera: Noctuidae) in Sarawak CMalaysjan Borneo). Bull, EnteJnol. 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