モンクロシャチホコおよびセグロシャチホコの幼虫の摂食量について

Abstract

林木の生育にあたえる食葉性害虫の影響を解明するには, 林木の反応を調査するとともに, defoli・atorとして作用する側の食葉性害虫の食害量-摂食量を明らかにすることは重要なことである。本報告は, 近年とくに公園や並木のソメイヨシノやヤマザクラを食害し, その被害が目立ってきたモンクロシャチホコの幼虫およびポプラを食害するセグロシャチホコの幼虫の摂食量を個体飼育により調査し, 脱糞量との関係を求めたものである。モンクロシャチホコ (Phalera flavescens Bremer et Grey) は1966年にはイトザクラ (Prunus subhirtella ver pendula (Maxim.) Tanaka), 1967年にはヤマザクラ (P. jamasakura Sieb., ex Koidz.), 1968年にはソメイヨシノ (P. yedoensis Matsum.) を餌として, セグロシャチホコ (Clostera anastomosis tristis Staudinger) はポプラ (Populus euramericana cv. I-154) を餌として1968年に飼育した。さらに, 1968年には両種の飼育とともに, オオケンモン (Apatele major Bremer) およびリンゴケンモン (A. incretata Hampson) をソメイヨシノでマイマイガ (Lymantria daspar Linne) をポプラで飼育した。調査結果をまとめるとつぎのようになる。1) 京都附近では, モンクロシャチホコは8月上旬 - 下旬に鰐化し, 幼虫期間約35日の後, 9月下旬 - 10月上旬に蛹化し, 蛹態で越冬し, 翌年の7 - 8月に羽化する。セグロシャチホコは4月から9月下旬までに5世代をくりかえし, 幼虫期間は15 - 23日, 蝋期間は4 - 12日と発生の時期により差がみられる。5世代目の成虫が産下した卵は年内には艀化せず卵態で越冬した (表-1, 図-1)。2) オオケンモン, リンゴケンモンの幼虫期はモンクロシャチホコとほぼ同時期で, 蛹態で越冬した。しかし9月までの経過は今回は調査しなかった。3) モンクロシャチホコ, セグロシャチホコともに幼虫期を5令または6令で経過し, 前者はほぼ半々であったが, 後者は6令までみられるものはすくなかった。両種とも雌雄はほぼ1 : 1である。4) 1頭当りの摂食量は, モンクロシャチホコでは, 雄は730 - 890cm_2, 5200 - 6200mg (ヤマザクラ), 680 - 770cm_2, 4700 - 5300mg (ソメイヨシノ), 雌は920 - 1030cm_2, 6400 - 7000mg (ヤマザクラ), 700 - 890cm_2, 5000 - 6200mg (ソメイヨシノ), セグロシャチホコでは, ポプラ葉で雄は80 - 170cm_2, 400 - 750mg, 雌は110 - 270cm_2, 590 - 1200mgとなり, 雌雄による差は著しい。5) マイマイガのポプラ葉摂食量は, 雄は520 - 540cm_2, 3000 - 3100mg, 雌は870 - 1440cm_2, 4900 - 8200mg, オオケンモンのソメイヨシノ葉摂食量は1160 - 1320cm_2, 7940 - 9040mg, リンゴケンモンのソメイヨシノ葉摂食量は420 - 760cm_2, 3000 - 5300mgとなった。6) 蛹化前の摂食量は非常に多く, 最終令での摂食量は, モンクロシャチホコでは全摂食量の80 - 90％, セグロシャチホコでは85 - 90％で, さらに, その前令期での摂食量を加えると, 前者で93 - 98％, 後者で96 - 98％となり, 最終令とその前令期での摂食量を調査し, 全摂食量を推定しても大きな間違いとはならない (表-3)。7) 摂食量と脱糞量との関係は, 両対数グラフ上で, ほぼ直線関係が得られ, その関係式はつぎのようになった。モンクロシャチホコでは (図-3, 4) ヤマザクラ葉摂食 log L_a=0. 99408 log D-0. 77996…(1) log L_w=0. 98500 log D+0. 09270…(3) ソメイヨシノ葉摂食 log L_a=0. 95116 log D-0. 55593…(2) log L_w=0. 99702 log D+0. 14344…(4) L_a : 摂食葉面積cm_2, L_w : 摂食葉絶乾重量mg, D : 脱糞絶乾重量mg, のようになり, 餌によりすこし差がみられた。セグロシャチホコでは年間をまとめると (図-5) log L_w=0. 94258 log D+0. 26487…(5) のようになった。しかし, 各世代別に求めると (図-6) 1, 2化期 log L_w=0. 94298 log D+0. 30423…(6) 3化期 log L_w=0. 93850 log D+0. 29727…(7) 4化期 log L_u=0. 94502 log D+0. 24700…(8) 5化期 log L_w=0. 94986 log D+0. 19468…(9) のようにそれぞれですこし差がみられるが, その勾配にはほとんど差はみられない。8) 同時期に同樹種を餌として摂食した場合, 摂食量と脱糞量との関係は, とくに種による差はみられずほぼ同じになった。すなわち, 5月 - 6月にポプラ葉を摂食したセグロシャチホコの1および2化期の幼虫とマイマイガの幼虫で, および9月 - 10月にソメイヨシノの葉を摂食したモンクロシャチホコ, オオケンモンおよびリンゴケンモンの幼虫で, 前者はセグロシャチホコの1および2化期での関係 (6式) でマイマイガもほぼ満足し (図-7), 後者はモンクロシャチホコでの関係 (4式) でオオケンモン, リンゴケンモンともにほぼ満足した (図-8)。9) 幼虫の体重と摂食量との関係は, 大分バラツキがみられるが, 摂食量は体重にほぼ比例するようである。しかし, モンクロシャチホコとセグロシャチホコの両種間では相当に大きな差があらわれた (図-9)。

In order to know fully the effects of leaf-eating insects upon the growth of forest trees, it is important that defoliation by leaf-eating insects and their feeding be investigated. With respect to this question, the authors deal with the results of individual breeding and feeding of the black-marked prominent (Phalera flavescens Bremer et Grey), the black-back prominent (Clostera anastomosis tristis Staudinger), the gypsy moth (Lymantria dispar Linne), the large dagger moth (Apatele major Bremer) and the apple dagger moth (A. incretata Hampson). These investigations were carried out from 1966 ~ 1968 at the Experimental Forest Station of Kyoto University: the black-marked prominent was bred on Prunus subhirtella var pendula (Maxim.) Tanaka in 1966, on P. jamasakura Sieb., ex Koidz. in 1967 and on P. yedoensis Matsum. in 1968, and in 1968, the black-back prominent and the gypsy moth were bred on Populus euramericana cv. I-154, and the large dagger moth and the apple dagger moth were bred on P. yedoensis Matsum. The results obtained from the investigations were as follows: 1. In Kyoto, the eggs of the black-marked prominent hatched in August and after passing through the larval stage in about thirty-five days they pupated in late September and early October. After hibernating during the pupal stage, the adult moths emerged in the following July and August (Table 1, Fig. 1). 2. The black-back prominent had five generations from April to late September. The period of their larval stage was 15 ~ 23 days and that of the pupal stage 4 ~ 12 days (Table 1, Fig. 1). 3. The larval stages of large dagger moths and apple dagger moths were almost the same as the larval stage of black-marked prominents. They hibernated during the pupal stage. 4. The larval stage of black-marked and black-back prominents terminated at the fifth or sixth instar, but in the case of black-back prominents, a few individuals completed the sixth instar. The emergence of males and females was about half and half in both species. 5. The total feeding leaf area in cm2 and dry-weight in mg per larva were, for the male black-marked prominent, 730 ~ 890cm2, 5200 ~ 6200mg (P. jamasakura Sieb., ex Koidz.), 680 ~ 770cm2, 4700 ~ 5300mg (P. yedoensis Matsum.), and for the female, 920 ~ 1030cm2, 6400 ~ 7000mg (P. jamasakura Sieb., ex Koidz.), 600 ~ 890cm2, 5000 ~ 6200mg (P. yedoensis Matsum.). For the male black-back prominent, the values were 80 ~ 170cm2, 400 ~ 750mg, and for the female, 110 ~ 270cm2, 590 ~ 1200mg. This shows the feeding of males was smaller in quantity than the females. And the total feeding leaf area and dry weight of the gypsy moth were for the male 520 ~ 540cm2, 3000 ~ 3100mg and for the female 870 ~ 1440cm2, 4900 ~ 8200mg; for the large dagger moth 1160 ~ 1320cm2, 7940 ~ 9040mg and for the apple dagger moth 420 ~ 760cm2, 3000 ~ 5300mg. 6. The feeding at the last instar before pupation was the greatest, because in comparison with the total, it amounted to about 80 ~ 90% in dry weight base for the black-marked prominent, about 85 ~ 90% for the black-back prominent. Furthermore, the feeding during the last and the previous instars was about 93 ~ 98% to the total in the black-marked prominent, about 96 ~ 98% in the other. Therefore, the total feeding can be estimated from the feeding during the last and the previous instars for these two species (Table 3). 7. The high correlations between the feeding leaf (area and dry-weight) and dry weight of the frass are shown through the straight lines on the logarithms, that is; black-marked prominent (Figs. 3 and 4) P. jamasakura Sieb, . ex Koidz.: log La=0.99408 log D-0.77996･･･(1) log Lw=0.98500 log D+0.09270･･･(3) P. yedoensis Matsum.: log La=0.95116 log D-0.55593･･･(2) log Lw=0.99702 log D+0.14344･･･(4) La: the feeding leaf area in cm2 Lw: the dry weight of feeding leaf in mg D: the dry weight of the frass in mg It seems that there is a difference in allometric relations between P. jamasakura Sieb., ex Koidz. and P. yedoensis Matsum. black-back prominent fed poplar (Fig. 6) the first and second generations: log Lw=0.94298 logD+0.30423･･･(6) the third generation: log Lw=0.93850 logD+0.29727･･･(7) the fourth generation: log Lw=0.94502 logD+0.24700･･･(8) the fifth generation: log Lw=0.94986 logD+0.19468･･･(9) Although there is a difference in allometric relations in almost all generations, the resulting lines were almost parallel. These correlations can also be applied to dead individuals at the larval stage as has been shown previously by studies done on the pine caterpillar (Dendrolimus spectabilis), the gypsy moth and the camphor silk moth (Dictyoploca japonica). 8. When leaf-eating insects feed on the leaves of the same tree-species during the same time, it seems that there is a high correlation between the feeding and the amount of the frass as shown by the same straight line on the logarithms. These correlations were observed in the following cases: the black-back prominent and the gypsy moth feeding on poplar from May to June (Fig. 7), and the black-marked prominent, the larger dagger moth and the apple dagger moth feeding on P. yedoensis Matsum. from September to October (Fig. 8). 9. It seems that the feeding is nearly proportional to the weight of a larva in the same species. But there was a great difference observed between the species of the black-marked prominent and the black-back prominent (Fig. 9).