]pn. ]pn. J Environ. Entomo l. Zoo l. 19 (3) : 115 -124 (2008) 環動昆第四巻第3号: 115 - 124 (2008) Artcle Artcle

Population Population dynamics of an invasive grub lepida (Cramer) that damages ornamental ornamental trees : the seasonal and annual fluctuations of the cocoon density

Hiroichi Hiroichi Sawada 1 )， Yuuki Hori 1 )， Satoshi Nisida 1 )， Takashi Matsumoto z) and Takayoshi Nishida 3)

1) 1) School of Environmental Science ，The University of Shiga Prefecture ，Hikone ， Shiga 522 】 8533 ， Japan 2) 2) Graduate School of Human and Environmental Studies ，Kyoto University ，Kyoto 606-8501 ， Japan

3) 3) Laboratory of Ecology ， Graduate School of Agriculture ，Kyoto University ，Kyoto 606 同 8502 ， Japan

(Received (Received August 28 ， 2008 ; Accepted October 21 ， 2008)

Abstract

We analyzed population dynamics of an invasive grub moth Parasa lepia α(Cramer) ( : ) in terms terms of the cocoon and adult density on various host plants consisting of 51 tree species of 404 individual trees at the the campus of the University of Shiga Prefecture ，Hikone ，Shiga ， western Japan during 5 years from 2003 to 2007. The cocoons occurred twice a year ， the first generation in middle July -middle August and the second generation in

middle middle September 悶 late October. After hibernating as the pre 回 pupae within the cocoons ， the adults of the second generation generation emerged during early June to early July in the following year. The mortality of cocoons was consistently higher higher in the second generation than in the first generation ，resulting in the very low density of adults in the second generation. generation. In the first generation ，however ， the survival rate of the cocoons decreased year by year from 91. 0 % in 2003 2003 to 45 .1 % in 2007. The population growth rate from the second generation adults to the first generation cocoons

(R j) was higher when the adult density was higher ，indicating the presence of the inversely density dependent processes processes in R j. As the consequence the cocoon density fluctuated violently year by year in the first generation. In contras t， the population growth rate between the first generation adults and the second generation cocoons (Rz) functioned functioned both density dependently and complementary with the adult density ，resulting in the exclusively stable cocoon cocoon density in the second generation. We discussed ecological mechanisms in particular agents of larval mortality that that were assumed to be responsible to the inversely density dependent processes and the density processes processes in R j and Rz ，respectively.

Key words: Parasa lepida (Cramer) ， Population dynamics ， Annual population fluctuation ， Density dependence ， Inversely Inversely density dependence

Introduction Introduction up to Kanto district (N akano ， 2003). P. lepida is regarded regarded as a serious pest of street trees and garden Parasa Parasa lepid α(Cramer)， (Lepidoptera: Limacodidae) trees ，and also as a noxious pest that gives pain in is is an invasive moth ， widely distributed in tropical- human skin. subtropical subtropical regions such as southern China ，south-east To establish an e妊'ective management system of a Asia ， ，and sub-Saharan Africa (Hirashima ， given pest it is necessary to understand ecological 1989 ; Zhang ， 1994). In Japan P. lepida was first mechanisms that cause the population changes recorded recorded in Kagoshima in 1921 ，thereafter expanding through quantification of mortality factors such as the the distribution range north-eastward in Kyushu and natural enemies as well as knowledge of the life Honshu ，and in 1980s frequent outbreaks occurred by history (Price and Waldbauer ， 1982 ; Levins ， 1986 ; defoliating defoliating persimmons and cherry trees (Oda and Nakasuji ，1997). Yamazaki et al. (1994b) examined the Hattri ， 1981). Recently ， the range expansion reaches cocoon density of P. lepida at 65 sites within Osaka ，

Corresponding Corresponding author : [email protected]

-115 Sawada eta l.

Kyoto and Shiga Prefectures ，and speculated that the and Hattori ， 1981). This species is a typical natural natural enemy was the major factor that determined polyphagous herbivore feeding on a wide range of the the distribution and abundance ， on the ground that p ， trees. For instance ，Yamazaki et al. (1994a) found the lepida lepida occurred exclusively in urban areas with few cocoon on all the 62 tree species of 31 families enemies ， but it was absent in its surrounding areas examined except for conifers ， the tulip tree with abundant enemies. On the basis of detailed Liriodendron tulipifera ， the southern magnolia Magnolia analyses analyses of the cocoon mortality at the campus of the grandiflora ，and the oleander Nerium indicum in Osaka ， University University of Shiga Prefecture in the suburbs of Kyoto and Shiga Prefectures. In the original Hikone ， Nishida et al. (2006) documented a very high distribution range such as India and south-east Asia ， mortality mortality due to bird predation on the cocoon during the host range consisted of 78 host plant species of winte r. At the same site Sawada et al. (2008a) 35 families including legumes (Fabaceae) ，palms conducted conducted detailed population censuses that covered (Arecaceae) ，and Euphobias (Euphobiaceae) (Robinson all all the developmental stages and documented following et al. ，2001). Additionally ， in India and south-east Asia results results : (1) Trichogramma dendrolimi Matsumura ，a P. lepi d， αis known as a pest of ，coconu t， coffee ， parasitoid parasitoid wasp was the major agent of the egg cacao and so on (Kalshoven ， 1981 ; Kapoor et al. ， mortality ， (2) the larval mortality in the first 1985 ; Jeyabalan and Murugan ，1996). generation generation was caused by generalist predators such as paper paper wasps ，spiders ， ladybird beetles and mantis ， but Study site and census trees the the mortality rate was fairly low ， (3) the larval The population censuses were conducted at the mortality mortality in the second generation was very high campus of the University of Shiga Prefecture (USP) primary primary due to a putative nuclear polyhedrosis virus (35 0 17' N ，136 0 15'E) locating in the suburbs of Hikone (NPV) and a fungal disease ，and (4) the occurrence City ， Shiga Prefecture. USP was founded in 1995 when of of the putative NPV was strongly density dependen t， approximately 70 species of trees were planted at 30 with with frequent occurrence in the year of the high larval ha of the campus. The campus was similar to a large density density and in the hosts of the great larval density. city garden ， in which a large number of P. lepida In In the present article we analyzed the seasonal and cocoon were observed. We chose 282 individual trees annual annual fluctuations of P. lepida population based on the of 36 deciduous species and 122 individual trees of 15 density density of the cocoon and the adult ，and the respective evergreen species as the census trees among a total of mortality mortality factors and survival rate of each generation approximately 70 tree species. The majority of on 404 host trees of 51 species over 5 years during deciduous species were Chinese tallow tree Triadica 2003 2003 and 2007. And also we interpreted the observed sebifera ，Yoshino cherry Prunus X yedoensis and seasonal seasonal and annual trends of P. lepida population in Japanese zelkova Zelkova serrata ，and that of evergrεεn relation relation to the egg and larval mortality documented in species were oaks Quercus myrsinaefolia and Q. our our previous studies (Sawada et al. 2008a ，b). and camphor laurel Cinnamomum camphora. On each census census tree we recorded the number of cocoon formed ， Materials Materials and Methods the mortality factors of the cocoons ，and the number of the the cocoons from which the adults emerged. To Parasa Parasa lepida (Cramer) standardize the number of tree species examined we P. P. lepida is a notorious pest of street trees and chose 10 individual trees for each tree species unless ornament trees particularly in urban areas. The larvaε ， the tree density was less than 10. forming forming a compact aggregation in the early stage ， feed on tree leaves. This species is also regarded as a Census of the cocoon density noxious noxious pest because contact with its larval spines can The cocoon density was examined every week cause cause dermatitis in humans (Oda and Hattori ， 1981 ; during which the larvae formed the cocoon ， middle Miyata ，1981). July 一late August for the first generation and middle

P. P. lepid αoccurs， twice a year in western ]apan with September early Novembεr for the second the the first generation adults in early to late ]une and the generation ， over 10 generations of 5 years ，from the second second generation adults in early August to middle first generation of 2003 to the second generation of September ，and hibernates as the cocoon stage (Oda 2007. To avoid double counting ， the cocoons were

-116 Population Population dynamics of an invasive grub moth

marked with water resistant pain t. The cocoon density other larvae pupated just above the cocoons and per per tree of a given generation (C1 and C2) was thus thereby prevented the emergence. By summing up the defined defined as the total number of the cocoons marked at number of the newly emerged adults at each census the the generation divided by the total number of the we calculated the date of 50 % adult emergencε ， census census trees. Similarly we calculated the date of 50% indicating the day when 50 % of adults emerged cocoon cocoon formation for each generation. The census area among the total num ber of the adults for each for for each census tree was limited to the tree trunk and generat lO n. branches branches less than 2.5 m at height because a majority From a small proportion of the cocoons produced of of the cocoons were formed there during July - August in 2006 and 2007 ， neither adults nor nor parasitoids emerged after the normal emergence Mortality Mortality factors during the cocoon stage and the period of August and September. We found that thesε adult adult density at emergence cocoons had univoltine life cycle ， the adults occurring We examined the density of newly emerged adults only one generation a year in June (Sawada et al. ， during the period from the start of the cocoon unpublished). Thus we regarded that the cocoons ， formation formation to the end of the adult emergence; middle produced in the first generation but no adults emerged July July - early September and middle September the by the end of September ，were of the univoltine life following following early J uly for the first and the second cycle and were excluded from the estimation of the generations ，respectively. The intervals of the censuses adult emergence rate of the cocoons of the first were one week for the first generation and one to generat lO n. three three weeks for the second generation in consideration of of the far longer cocoon stage in the second Estimation of population growth rate generation. generation. We recorded the number of the cocoons Here ， the population growth rates of the first and killed killed by each mortality factor and the number of the the second generations were defined respectively as R1 cocoons from which the adults emerged for each (=C1/ Ao) ， the rate of the cocoon dεnsity of the first census tree. By summing up all these data we generation (C1) to the adult density of the second estimated the cocoon mortality per tree and the (over wintering) generation (Ao or A2) ，and as R2 density density of newly emerged adults per tree for each (=C2/ A1) ， the rate of the cocoon density of the second generation generation (A1 and A2). generation (C2) to the adult density of the first A considerable proportion of the cocoons had generation (A1). By comparing R1 and R2 we emergence holes without exuviae remained ，which analyzed patterns of the seasonal and annual

were regarded as being killed by birds. This was fluctuations of the P 目 lepida population. because because 1) observations by field-set video recorders revealed revealed that small birds such as great tit Parus major Results manipulated manipulated to open emergence holes of the cocoons in addition addition to leaving various types of predation scars ， The seasonality of the cocoon formation and the adult and preyed on the pupae by excavating them ， 2) the emergence laboratory laboratory rearing of the cocoons confirmed that the In Table 1 ， the date of 50 % cocoon formation and of adults adults always left the exuviae at the emergence holes ， 50 % adult emergence were described as well as the and 3) the cocoons with emergence hole but without average period of the cocoon stage (the period exuviae exuviae occurred mostly during winter when no adult between the above two dates) over 5 years ， 2003 emergence occurred. Consequently we regarded only 2006. In the first generation of 2003 the larvae formed the the cocoons with both the emergence holes and the the cocoon approximately over one month ，from July exuviae exuviae as those of successful adult emergence ，and 21 to August 25 ，with the date of 50% cocoon thereby estimated the proportion of the adult formation (tt) on August 5. The adult emergence emergence for each generation (Sl and S2). Other occurred during August 13 and September 8， with the minor mortality factors of the cocoons were parasitoid date of 50 % adult emergence (t2) of August 22 ， wasps ， diseases (blackened to death within the indicating the average period of the cocoon stage (t1 cocoons cocoons without predation scars) ，emergence failure t2) as 17 days (Table 1 ). Over 5 years during 2003 and so on. The emergence failure often occurred if 2007 ， the date of 50 % cocoon formation and the date of

117 117 Sawada el al

Table 1 The dates of 50% cocoon formation (t j)， of 50% adult emergence (tz) ，and the average periods periods (days) of the cocoon stage (t z -t 1) in the first and the second generations of Parasa Parasa Lepi d， αfrom 2003 to 200 7， First First Generation Second Generation tj tj tz tz- tj tj tz t2- tj

2003 2003 5，Aug 22.Aug 17 l1. 0ct 11. Jun 243 2004 2004 27 .J ul 16.Aug 20 7.0ct 10.]un 245 2005 2005 2.Aug 20.Aug 18 9.0ct 16.]un 249 2006 2006 3.Aug 25.Aug 22 5.0ct 17.Jun 254 2007 2007 6.Aug 27.Aug 21 12.0ct

Table Table 2 The adult density per tree of the second (over wintering) generation (A o)， the population growth rate (R j)， the cocoon density (C j)， the adult emergence rate from the cocoon (Sj) ， the average rate of adult 日 nergence from the cocoon per 10 days (Sj *)， and the adult density (A j)， of the 五rst generation from 2003ω2007. A 。(=Az) Rj(=Cj/A o) Cj Sj (=Aj/C j) Sj* A j 2003 2003 1. 29 0.910 0.946 1.1 71 2004 2004 0.062 7.56 0.4 7 0.804 0.897 0.376 4.61 4.61 O. 21 0.627 0.771 0.1 29 尺 つれ】門EUQU52 2006 2006 0.1 76 45.77 8.04 0.653 0.824 υnu--一 2007 2007 0.084 20.88 1. 76 0.451 0.684 i 一日一円 一一 UHUi4497 mean 0.080 13.5 1.1 2 0.670 0.819 .. aっ口一 variance# variance# 0.065 0.1 99 0.365 0.014 0.003 d #: Variances were calculated after log-transformation.

Table Table 3 The adult density per tree of the first generation (A j)， the population growth rate (R z)， the cocoon density density (C z)， the adult emergence rate from the cocoon (Sz) ， the average rate of adult emergence from the cocoon cocoon per 10 days (S 引， and the adult density (Az) ， of the second generation from 2003 to 2007.

A j Rz(=CzI AJ C z Sz (=A 2/C z) Sよ Az 2003 2003 1.1 71 1. 31 1. 54 0.040 0.876 0.062 2004 2004 0.376 6.4 1 2 .4 1 0.018 0.850 0.045 2005 2005 0.1 29 23.94 3.08 0.057 0.891 0.176 2006 2006 5.255 0.42 2.22 0.038 0.879 0.084 2007 2007 0.792 4.52 3.58 mean 0.749 3.2 9 2.46 0.036 0.874 0.080 variance# variance# 0.357 0.4 50 0.020 0.042 0.000 0.065 #: Variances were calculated after log-transformation

一一 118 一 Population Population dynamics uf an invasive grub molh

50 50 % adult emεrgence were July 27 - August 6 and (F=2.63 ，df 口 3，4， p=0.19 ，F 市 test) due to the small August 16 - August 27 ，respectively ，and thεaverage sample size despite of the five years of the study periods periods of the cocoon stage were 17 - 22 days (Table period. ). 1 ). We excluded the cocoons of the univoltine life The adult emergence rate from the cocoons in the cycle ，from which no adults emerged by the end of first generation (Sl) ranged 0.4 51 to 0.910 ， with the September ，from the above calculations. geometric mean of 0.670 over the five years. It is In In the second generation of 2003 ， the cocoon noteworthy that Sl gradually dropped over the five formation formation occurred during September 22 - October 26 ， years (Wald's X2 =256.95 ，df=4 ， p

11 11 in 2003 and June 11 in 2004 ，respectively ，indicating the first generation (t=4.35 ，df=3 ，p=0.02 ， paired t同 the the average period of the cocoon stage (b - t2) as 243 test). In the first generation ，similarly as the cocoon days days (Table 1 ). Over 5 years from 2003 to 2007 ，tl density ，the adult density fluctuated largely ， as and tz were October 5-12 and June 10 17 in the indicated by the large log-transformed variance of subsequent years ，with the average period of the 0.357. cocoon cocoon stage of 243 - 254 days (Table 1 ). Patterns Patterns of population growth in the second generation Patterns Patterns of population growth in the first generation Table 3 shows the population parameters in the In In Table 2 ， the adult density of the second (over second generation during 2003 - 2007 ; the adult wintering) wintering) generation ，Ao (= A2) ，and the cocoon density of the first generation ，Al ， the density of the density density and the adult density in the first generation ， Cl cocoons and the adults in the second generation ， Cz and Al ，respectively ，were described. Using these and A2 ，respectively ， the population growth rate in the densities ， the population growth rate Rl (=C1I Ao) and second generation ， R2 (=C21 Al) ，and the survival rate the the emergence rate of the adults ， Sl (=A !l Cl) were of the cocoon in the second generation ， Sz (口 AzICz) . also also calculated (Table 2 ). In addition ， as indices to Similarly as in the analyses of the first generation ， the examine the relative magnitude of variations of these geometric means of these population parameters and population population parameters ， the geometric means and their their log-transformed variance were also shown. log-transformed log-transformed variances were described (Table 2 ). The adult density per tree just before the start of Moreover ， the average rate of cocoon survival per 10 the second generation (Al) was on average 0.749 ，and

days ， S* (= S'o ノL : L denotes the average period of the was 0.129 at minimum in 2005 and 5.26 at maximum in cocoon stage) was shown ，considering that the 2006 ， with the magnitude of var 匂 tion of

average period of the cocoon stage was markedly (=5.26/0 .1 29). The log 同 transformed variance was 0.357. different different between the first and the second generations. The population growth rate (Rz) was 3.2 9 on average ，

The adult density per tree of the over wintering ranging from 0.4 2 to 23 ゑ The cocoon density (C2) ， as generation generation (Ao) was on average as 0.080 ，smallest as the product of Al and R2 ，was 2.46 on average ，and 0.045 0.045 in 2005 and largest as 0.176 in 2006 ，with the was quite stable over the five years ，fluctuating from degree degree of variation of 3.9 (=0 .1 76/0.045) over the four 1. 54 to 3.58 ， with the variability of 2.31 (=3.58/1.54)

years. years. The log 目 transformed vari 呂nce ， as an index of the Consequently ， the log 【 transformed variance was 0.020 ， variability ，was 0.065. The population growth rate (Rl) far smaller than that in the first generation adults fluctuated fluctuated largely from 4.61 to 45.8 ， with the average of (F= 12.25 ，df=4 ムp=0.02 ; F-test) (Table 3 )， indicating 13.5. 13.5. The cocoon density in the first generation (Cl) ， the presence of the density dependent stabilizing as as the product of Ao and Rl ，was on average 1.1 2 and processes in the second generation fluctuated fluctuated from 0.21 to 8.04 ， with the magnitude of 39.2 The adult emergence rate from the cocoons in the (=8.04/0.21). (=8.04/0.21). The log-transformed variance was 0.365 second generation (S2) was very low ， 0.036 as the (Table (Table 2 ). These results indicated that the cocoon geometric mean over the four years ， ranging from density density of the first generation (Cl) fluctuated more 0.018 to 0.057. The difference between the first and the largely largely than the adult density of the over wintering second generations (Sl VS. S2) was statistically

generation generation (Ao) ，though not statistically significant significant (z= 】 30.04 ，df=6 ，p

-119 一 Sawada etal

difference difference between the generations ，however ，may be variance of A2 was very small ， 0.065 on average ， largely largely ascribed to the large difference in the period of indicating the stable adult density in the second the the cocoon stage between the two generations ，on the generation over the years ， similarly as that of the ground that the standardized rate per 10 days (SI* cocoon density (C2) as described above. and S2*) did not differ significantly (t= -1.1 4，df=4 ， p=0.32 ， paired t-tes t， after being arcsine transformed) Comparisons of annual fluctuations of the first and (Tables (Tables 2 and 3). The adult density of the second second generations generation generation (A2) was 0.080 per tree on average ，and Fig. 1 shows the annual fluctuations of the adult and was smaller than that in the first generation (Al) the cocoon density ， Ai-l and Ci， respectively ，the though not statistically significant (t= -2.37 ，df=3 ， population growth rates ， Ri (=C/ Ai 1) ，and the adult p=0.10 ， paired t-test). Moreover ， the log-transformed emergence rate from the cocoon ， Si (= A i/ C) ， in the

First First Generation Second Generation

1.0 1.0 1.0 .. ~.. 0.0 ::;:: .. 0.0 3-10 トー〆/九九 .3 -1.0

2.0 2.0 叩 2.0

2.0 2.0 2.0 .. 0:: .. 1.0 ~可 1i:! .. 1.0 .3 .3 0.0 .3 0.0

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o 1.0 ~ 1. 0 ...... 3 .3 0.0 300

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nUnununu nυeBq'ιnυnUAυpz'aaa NωF-a の凶 週'aapaaazaL 同 唱?内 E.』 0 0」 」 ，aEL 」一寸---←ーー企 4

三日日ト .. .. I .3 .3 -1. 0 ~ ;1:[ 一一 2003 2003 2004 2005 2006 2007 Year Year

Fig. Fig. 1 Yearly changes in log-transformed Parasa lepida adult densities per tree (Ao ，Al ，Az) ， the population growth rates rates (RJ ，Rz) ， the cocoon densities per tree (Cl ， C2) and the adult emergence rate from the cocoon (SI ， Sz) in the the first (l eft-handed) and the second (right-handed) generations from 2003 to 2007.

-120 一 Population Population dynamics of an invasive grub moth

first first (i =l) and the second (i =2) generations during

2003 2003 - 2007 ， in the logarithm scale. The cocoon density ， Log Ai = Log C+ Log Si (i =1 or 2) C ，is expressed as the sum of the adult density in the

previous previous generation ，Ai.1 ，and the population growth Fig 圃 1 (left) illustrates the large annual fluctuations rate rate in that generation ，Ri ， in the logarithm scale of C1 ，which is expressed as the sum of fluctuations of Ao and Rl ， in the logarithm scale. There was a positive

Log C = Log Ai.l+ Log Ri (i =l or 2) correlation between Ao and Rl (t=6.06 ，df=2 ，p く0.05 ， regression regression analysis) (Fig. 2，upper left) ， implying that In In a similar manner ， the adult density ，Ai ，is expressed both of the annual fluctuations were enhanced through as as the sum the cocoon density ，Ci， and the adult the dεvelopmental processes. In other words ， the emergence rate from the cocoons ，Si. population growth rate R1 was inversely density

First First Generation Second Generation

2.0 2.0 2.0 '06 '06 ;+ ;+ v.mw¥ 1. 5 '07 +， ， 1.5 、 / ¥ 1.0 1.0 / ¥倒 FN NN 1.0 比国 ル '04 協同 、. ¥ WUA'¥1¥1 oJ O 4 」 ¥ 0.5 0.5 '05 0.5 ¥. な ¥ ¥ 。。 b= 1. 17 0.0 ¥ b= 一1.10 ¥ p く0.05 p く0.01 ¥UA' 明 。。

一0.5 ー0.5 -2.0 -2.0 一1.5 一1. 0 一0.5 0.0 -1. 0 -0.5 0.0 0.5 1. 0 Log Log AO Log A1

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Fig. Fig. 2 Relationships between the Parasa lepida population growth rates (Rl ， R2) and the adult densities per tree of the the previous generations (Ao ，Al ; upper) ，and between the adult emergence rate from the cocoon (Sl ， S2) and the the cocoon densities (C1 ， C2 ; lower) in the first (l eft-handed) and the second (right-handed) generations from 2003 2003 to 2007.

121- Sawada etal

dεpendent to the adult density in the previous words ，therεwer 己 the positive feedback processes generation generation (Ao). Indeed ，Ao was high and low ，and Rl which destabilized the population density ，between the was high and low ， respectively in 2005 and 2006 ， adult density (Ao) and the subsequent population resulting resulting in the large annual variations documented in growth rate (Rl) in the first generation ， further

Fig 且 1 (l eft) increasing the annual fluctuation of the cocoon density In In contrast ， the annual fluctuations of SI were (CI). On the other hand ， the intense negative feedback exclusively exclusively stable ， resulting in the closely similar processes ， implying the stabilizing effec t， occurred in annual annual fluctuations between Cl and Al (Fig. 1，left). the second generation ， thereby greatly stabilizing the No sign i:fi cant relation was detected between Cl and the cocoon density in the second genεration (C2). adult adult εmergence rate from the cocoons (Sl) (z= -0.47 ， The population growth rate in the i-th generation df=2 ，p=0.64 ，GLMM) ，though SI gradually decreased (Ri) is expressed by the product of following three

annual annual from 2003 to 2007 (Fig 且 2， lower left) component factors ; the numbεr of eggs laid per adult ， In In the second generation ， the cocoon density (C2) the survival rate of eggs and the proportion of larvae was very stable over the years (Fig. 1， right). In that reached the cocoon stage contrast contrast to the first generation ， there were density dependent dependent processes that greatly stabilized C2 : Al and Ri =C し/Ai ー1 =E i/ Ai.l x L/Ei X C/Li

R2 were negatively correlated each other (t=8.96 ， = Fi X S (E i) xS (Li) df=3 ，p く0.01 ; regression analysis) (Fig. 2，upper right). right). Indeed ，R2 was high and low respectively in Here ，Ei ，L ，Fi ， S (Ei) ，and S (Li) denote the egg density 2005 and 2006 when AI were low and high ， in the i-th generation ， the larval density ， the number of respectively respectively (Fig. 1 ，right). The annual fluctuations of eggs laid per adul t， the survival rate of eggs ，and the the the adult density of the second generation (A2) ， being survival rate of larvae ， respectively. By taking expressed as the sum of those of C2 and S2 ，were logarithm the formula can be described as follows closely closely similar with those of S2 ， because C2 was very stable stable over the years (Fig. 1 ，right). Log Ri = Log Fi + Log S (E i) + Log S (Li)

Discussion Thus in the logarithm scale ， the population growth rate rate in the i-th generation is the sum of the realized The annual fluctuation of the cocoon density in the fecundity per adul t， the survival rate of eggs ，and the

first first and the second generations exhibited the sm 喝 vival rate of larvae. markedly different patterns ; the large variability in Sawada et al. (2008a) documented the detailed the the first generation whereas the contrasting stability population processes of P. in the same in in the second generation ， being indicated by the log- during 2005 - 2007 ， and suggested the transformed transformed variations (Fig. 1). In the first generation density dependent mortality of larvae in the first of of 2006 when the cocoon density was highes t. more generation on the ground that (1) at the scale of the than than 100 cocoons were found on 6 host trees ， such as local population ， the larval mortality was lower in the T. T. sebifera and the matsumurae maple Acer palmatum year of higher larval density as in 2006 ，and (2) var. var. matsumurae ，呂mong 404 census trees. Virtually within a year the larval mortality was lower in host almost almost all the leaves were consumed up in these 6 trees of higher larval density. As the larval mortality trees trees by intensive feeding of a large number of the old factors in the first generation ， predation by paper instar instar larvae. Contrastingly ，no such serious feeding wasps ，spiders ，and ladybird beetles ，a fungal disease ， damage was observed in the second generation ，even and a storm were identified (Sawada et al. 2008b). though the cocoon density itself was on average 2.2 Hence ，it is necessary to quantify the degree of the times times higher (but not statistically significant) in the inverse density dependence for each of the above second second generation than in the first generation factors. The analyses of the population dynamics revealed In contras t， the larval mortality was strongly density that that the population growth rate was inversely density- dependent in the second generation: The larval dependent in the first generation ，but was density- mortality was substantially higher in the year and the

dependent dependent in the second generation (Fig 闘 1). In other trees of the higher larval density (Sawada et al 目

-122 Population Population dynamics of an invasive grub moth

2008a). 2008a). As the major mortality factor nuclear Butler. J. Jp 凡 For. Soc. 41 (1) : 4-10. (in Japanese). polyhedrosis polyhedrosis virus (NPV) ， though not precisely Levins ， R. (1986) Perspectives in integrated pest identified identified in a strict sense ，was suggested (Sawada et management : from an industrial to ecological al. al. 2008b). We speculated that the density dependent model of pest managemen t. In “Ecological theo η occurrence occurrence of the presumed NPV realized the negative and integrated pest management practice" (Kogan ，M. correlations correlations between the adult density (Al) and the ed) ， pp. 1- 18 ，J ohn Wiley & Sons ，N ew Y ork. subsequent subsequent population growth rate (R2) ，and thereby Miyata ， A. (1981) On Parasa lepida Crame r. 01 greatly greatly stabilized the cocoon density in the second Niho 6: 21- 23. (i n Japanese) generation. generation. In this context ，it is interesting to refer Nakano ， K. (2003) Distribution of blue striped nettle that that the density dependent mortality due to NPV grub ，Parasa lepida (Cramer) (Lepidoptera: plays plays a critical role to put an end to outbreaks of Lim 呂codidae) ， in Kanto District. House and forest forest pests ， such as the gypsy moth ， Lymantria dispar Household Insect Pest 24 : 61- 62. (i n Japanese) (Linnaeus) (Linnaeus) (Koyama and Katagiri 1959 ; Stairs 1971 ， Nakasuji ， F. (1997) pest Integrated management. Yokendo 1972) 1972) . Lt d. ，Tokyo ， 273 pp. (i n Japanese)

Other than the larval mortality ， the population Nishida ，S. ， Y. Araki and 日 Sawada (2006) Seasonal growth ratεmay be affected by either the fecundity population changes of the blue striped nettle grub per adult or the 邑gg surviva l. It is necessary to moth Parasa lepid α(Cramer).， Ann. Rept. Kansai Pl. quantify quantify the relative contributions of these two factors Prot. 48 : 115 - 117. (i nJ apanese) in in addition to the larval mortality ， and their Oda ， M. and I. Hattori (1981) The bluestriped interactions interactions to understand fully the ecological (greens 出ped) ne 杖le grab ，La to 初旬i必 (Cramer) :A mechanisms that may bring the density dependent new pest of J apanese persimmon. Plant Protection and the inversely density dependent mortality 35 : 401 - 405. (i n Japanesε) observed observed in P. lepida. Price ， P. W and G. P. Waldbauer (1982) Ecological aspects aspects of pest managemen t. In ソntroduction to Acknowledgements insect pest managemen t" (Metcalf ， R. L. and W. H Luckmann eds) ， pp. 33 - 68 ，John Wiley & Sons ， We would like to thank Y. Araki ， Y. Mizuno ， Y. New York. Masumoto ， T. Kato ， S. Shimomura and M. Kida for Robinson ， G. S. ， P. R. Ackery ，1. J. Kitching ， G. W their their kind support with the field survey. Beccaloni and L. M. Hernandez (2001) Hos 伊lants 01 01 the moth and butte ポ y caterpillars 01 the Oriental References Region. The Natural History Museum ，London Sawada ，Hη y. Masumoto ， T. Matsumoto and Hirashima ， Y. (1989) A check list 01 Japanese insect. (2008a) Comparisons of cocoon dε Entomological Entomological Laboratory ， Faculty of Agriculture ， survival processes of the blue-striped nettle Kyushu University ， Fukuoka. 1767 pp. moth Parasa lepida (Cramer) betwεen the Jeyabalan ， D. and K. Murugan (1996) Im pact of variation deciduous and evergreen trees. Jpn. J. Environ. in in foliar constituents of Mangifera indica Linn. on Entomol. Zool. 19 : 59 - 67. consumption and digestion efficiency of Latoia Sawada ，H. ，S. Shimomura ， T. Nishida and T. Matsumoto lepida lepida Crame r. Ind. J. Exp. Biol. 34 : 472 - 474. (2008b) Causes of larval mortality in relation to Kalshoven ， L. G. E. (1981) Pests 01 crops in Indonesia. host plant quality in the invasive grub moth ， (Revised (Revised and translated by P. A. van der Laan) Parasa lepid α(Cramer). Jpn. J. Environ. Entomol. PT. PT. Ichtiar Baru ，Jakarta. 701pp. Zool. 19 : 69 -78. Kapoor ， K. N. ，S. R. Dhamdhere and S. V. Dhamdhere Stairs ， G. R. (1971) Use of viruses for microbial control (1985) (1985) Bionomics of the slug caterpillar ， Latoia of insects. In “ Microbial Control olInsects and Mites" lepida lepida (Cramer) (Lepidoptera: Limacodidae) on (Burges ， H. D. and N. W. Hussey eds) ， pp. 97 mango. よ Entomol. Res. 9: 235 - 236. 124 ，Academic Press ，London ，New Yor k. Koyama ， R. and K. Katagiri (1959) On the virus disease Stairs ， G. R. (1972) Pathogenenic microorganisms in of of Lymantri αルmida Butler I. On a virus epizootic in the regulation of forest insect populations. Annu an out breaking population of Lymantria lumida Rev. Entomol. 17 : 355 - 372.

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Yamazaki ，K.， T. Kitamoto and K. Nakatani (1994a) Host plant selection of the blue 回 striped nettle grub

Host Host plant selection of the blue 回 striped nettle grub moth Parasa lepida (Cramer) 2. Nature Study 40 : moth Parasa lepida (Cramer) 1. Nature Study 40 : 43 - 46. (in] apanese)

20 20 23. (i n ]apanese) Zhang ， B. (1994) lndex of Economically lmportant Yamazaki ，K.， T. Kitamoto and K. Nakatani (1994b) Lepidoptera. CAB Internationa l， U K.

緑化害虫ヒ口ヘリアオイラガの個体群動態:融密度の季節的年次的変動

沢田裕一 1) ・堀祐規 1) 西田哲 1) ・松本崇 2 )西田隆義 3) 1 )滋賀県立大学環境科学部生物資源管理学科 2 )京都大学大学院人間環境学研究科相関環境学専攻 3 )京都大学大学院農学研究科見虫生態学研究室

滋賀県彦根市にある滋賀県立大学構内において， 2003~2007 年の 5 年間， 51 稜 404 株の樹木を対象に，ヒロヘリア オイラガの繭と羽化成虫の調査を行い，個体数の季節的年次的変動様式を解析した.繭は年 2 回発生し，第 1 世代繭は 7 月中旬 ~8 月中旬に形成された.第 2 世代繭は 9 月中旬 ~10 月下旬に形成され，そのまま越冬して，翌年の 6 月上旬 ~7 月上旬に羽化した.第 1 世代繭の羽化率は， 2003 年の 91.0% から 2007 年の 45 .1%まで，年を経るにつれ年々低 下する傾向が認められた.第 2 世代繭の羽化率は， 4 年間で 1.8%~5.7% まで変化し，第 1 世代繭の羽化率に比べ著し く低く，そのため，越冬後の第 2 世代成虫密度は低いレベルに抑えられた.第 2 世代(越冬世代)成虫期から第 1 世代

繭期への個体群増加率 R1 は，成虫密度の増加に伴って上昇する傾向，すなわち R1 に密度逆依存的な過程が作用するこ とが示唆され，第 1 世代繭密度の年次変動は激しく変化することが明らかになった.他方，第 1 世代成虫期から第 2 世 代繭期への個体群増加率 Rz は，成虫密度の増加に伴い減少する傾向，すなわち Rz に密度依存的な過程が作用すること

が示唆され，その結果，第 2 世代繭密度の年次変動は著しく安定化することが明らかになった. R1 と Rz に作用する密 度逆依存的，及び密度依存的な過程のメカニズムとして，特に幼虫期に働く死亡要因との関連について考察した.

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