外国産マツ属の虫害に関する研究 : 第5報 マツバノタマバエの加害について

Abstract

マツバノタマバエ (Thecodiplosis japonensis) が日本のアカマツ, クロマツを食害し, 針葉基部に虫癭を形成することはよく知られ, 2, 3の外国産マツをも食害することはすでに知られている。本報告には, 京都大学農学部附属演習林の上賀茂, 白浜, 徳山の3試験地に育てられている外国産マツ属について, マツバノタマバエの寄生を, その虫癭が形成されているかどうかで判定して調査した結果がとりまとめられている。さらに, マツ属の交雑育種の結果, 比較的交雑可能なクロマツを雌性親としたタイワンアカマツ (P. massoniana) とのF_1雑種の被害の状況をも, 両親と比較して調査した。1. 調査された65種 (変種およびF_1雑種を含む) のうち, 22種のマツ属にマツバノタマバエが加害しているのを確認した。被害の激しかった種は, タイワンアカマツとF_1雑種の数個体で, 針葉の70％ - 90％が加害されていた。ついで, P, nigra, P. tabulaeformis, P. thunbergiiおよびP. densifioraにやや被害が目立つ個体があったが, その他の種では被害は軽かった (表-1)。2. P. khasyaを除く21種の被害はすべて2針葉のもので, さらに, Critchfietd & Little, Shawおよび石井がマツ属を分類した, sylvestres 亜節または Lariciones 亜節に被害種が集中し, マツバノタマバエの寄生とマツ属の感受性が, このマツ属の分類と非常に高い相関があることがわかった (表-3)。3. 幹の新梢主軸と側軸では, 前者の被害が激しいことが明らかになった (図-1)。4. 新梢主軸の上下による被害は, 上部が激しいもの, 下部が激しいもの, 中部の激しいもの, 平均しているものなど, いろいろな例がみられ, 一様の傾向はみられなかった (図-2)。5. クロマツ, タイワンアカマツ, 両者のF_1雑種では, 徳山試験地における針葉被害率の3年間の調査で, 常に, F_1雑種の被害が最も激しく, ついでタイワンアカマツ, クロマツの順となった (図-3)。さらに, 上賀茂試験地において, 同様の3種の林分にリタートラップを設けて, 2年間調査した結果, マツバノタマバエの落下幼虫, リターに含まれる被害針葉ともにF_1雑種林, タイワンアカマツ林, クロマツ林の順となり, 徳山試験地の結果と一致した (表-4, 図-4, 5)。6. クロマツとF_1雑種が混植されたまま大きくなった苗畑で, 両者の被害は, F_1雑種がクロマツのほぼ2倍となり (表-5), F_1雑種のマツバノタマバエに対する高感受性が明らかになった。

It is well-known that the needles of Japanese red pine (P. densiflora) and black pine (P. thunbergii) are infested with the larvae of Japanese pine needle gall midge (Thecodiplosis japonensis). The attacks of Japanese pine needle gall midge upon foreign pine species had been observed for three years, from 1975 to 1977 at the three Experimental Stations of Kyoto University Forest----Kamigamo (Kyoto prefecture), Shirahama (Wakayama prefecture) and Tokuyama (Yamaguchi prefecture). The results obtained from the investigations were as follows: 1. Twenty-two pine species (including varieties and F1 hybrid) were infested with the larvae of Japanese pine needle gall midge and the development of galls were observed in the needles of these pine species (Table 1). And the other pine species, forty-three pines (including varieties), were not infested (Table 2). 2. P. massoniana and F1 hybrid of P. thunbergii (♀) × P. massoniana (♂) were severely infested with this gall midge but the other pine species were slightly infested. In the case of severe damaged trees of P. massoniana and F1 hybrid, 70~90% of needles were infested, in P. nigra, P. tabulaeformis, P. thunbergii and P. densiflora gall-formed needles were between 5% and 50% of the total needles. And only 0~5% of needles were infested in the other damaged species. 3. All gall was formed in the binate needles in a fasicle except the ternate needls in a fasicle of P. khasya. 4. Any gall was not observed in pine species of five needles in a fasicle in these investigations. 5. Pine species infested with this midge have been classified into Subsection "Sylvestres" by Critchfield & Little and into Subsection "Lariciones" by Shaw and Ishii except P. coulteri and P. radiata (Table 3). Therefore, it seems that the pines classified into these Subsection, "Sylvestres" or "Lariciones", are infested with Japanese pine needle gall midge. 6. Generally, the infestation with this gall midge upon the top of the crown is severe than the bottom of the crown. Percentage of infested needles to the total in the leading shoot on terminals of stem was higher than that of lateral shoots of P. thunbergii, P. massoniana, F1 hybrid of P. thunb. (♀)×P. masso. (♂) and P. densiflora (Fig. 1). 7. F1 hybrid obtained from crossing of P. thunb.(♀)×P. masso. (♂) were infested with this gall midge in the progny test stand at Kamigamo and Tokuyama. At Tokuyama, average of damage percentage of needle in the leading shoot of F1 hybrid was 36.0% in 1975, 36.8% in 1976 and 41.6% in 1977. The other hand, these values were respectively 4.7%, 5.4% and 6.0% in P. thunbergii and 7.1%, 8.5% and 18.3% in P. massoniana in each year. 8. Numbers of fallen larvae of Thecodiplosis japonensis caught in trap in a season from November of 1976 to April of 1977 were 113 individuals per m2 in P. thunbergii stand, 1275 in P. massoniana stand and 2278 in F1 hybrid stand, and were respectively 121, 693 and 1337 from November, 1977 to April, 1978 at Kamigamo (Table 4 and Fig. 4). 9. The gall formed needles caught in litter-trap were measured through the year in three pine stands, P. thunbergii, P. massoniana and these F1 hybrid. Through the two years, F1 hybrid stand had the largest number of damaged needles in comparison with the three stands (Table 4 and Fig. 5). 10. It seems that F1 hybrid of P. thunb.(♀) P. masso. (♂) may be infested severely with Japanese pine needle gall midge as compared with the parents.