外国産マツ属の虫害に関する研究 : 第3報 スジコガネ成虫の摂食について

Abstract

スジコガネの成虫は針葉樹類の針葉を食害し, スギ, ヒノキ, カラマツなどを加害することはよく知られている。しかし, マツ属では, アカマツ, クロマツ, テーダマツを摂食するが, 被害報告はすくない。本報告は, 京都大学農学部附属演習林上賀茂試験地および白浜試験地に植えられている外国産マツ属に対するスジコガネ成虫の摂食を調査し, さらに, 白浜試験地のテーダマツ林で, 1968年以後スジコガネ成虫の生息状況, 食害量などを, トラップで虫糞を集めて推定し, その結果をとりまとめたものである。1. スジコガネ成虫の発生は, 6月中旬 - 8月中旬, その最盛期は7月上 - 中旬で, 白浜試験地では連年発生しているが, 1969年, 1971年, 1973年, 1975年に多数発生した。2. スジコガネ成虫が摂食したマツ属は, 上賀茂試験地では, P. banksiana, P. muricata, P. virginiana, P. pungens, P. rigida, P. echinataで, とくにP. muricataの被害が激しかった。白浜試験地では, P. elliottii, P. rigida, P. taedaであった。3. スジコガネ成虫の摂食量と脱糞量の関係は, F=1. 143 D F : 摂食量乾重 (mg), D : 脱糞量乾重 (mg) となり, 脱糞量の1. 143倍で摂食量が推定できる。4. スジコガネ成虫が摂食する時に, 利用せずに切り落すテーダマツ針葉は, 摂食量の約2. 3倍にも達する (図-1)。5. 白浜試験地のテーダマツ林に発生したスジコガネ成虫の体重 (乾燥重量) は, 90 - 210mgのものが大部分であった (図-3)。6. テーダマツ林におけるスジコガネ成虫の脱糞量は, 多く発生した年でも, 乾燥重量でhaあたり10 - 26kgで, 調査林分によって差がみられた (表-2)。7. スジコガネ成虫の7月上旬の個体数を脱糞量より推定した結果, 調査林分を平均して, haあたり1972年は2000匹, 1973年は10400匹, 1974年は2000匹, 1975年は13100匹で, 最大値はD林分で1975年に16900匹と推定された (図-6, 7)。8. 1968年から1975年のスジコガネ成虫の年間食害量は, 最大値でも133kg/haで, 林分葉量に比べて非常にすくなく, テーダマツの生育には影響をあたえていない (表-4)。

It is well-known that the needles of coniferous trees are infested with the adult of striated chafer (Anomala testaceipes). Many damages of Japanese cedar (Cryptomeria japonica), Japanese cypress (Chamaecyparis obtusa) and Japanese larch (Larix leptolepis) by striated chafer are reported, and on the pine genus, there are a little. In 1963, the feeding of the adult of striated chafer upon the imported pine-species in Japan were observed at Kamigamo Experiment Station of Kyoto University Forest in Kyoto prefecture. And at Shirahama Experiment Station in Wakayama prefecture, feeding upon the foreign pine species and grazing by the adult of striated chafer were investigated for eight years, from 1968 to 1975, in Loblolly pine stands (Table 1). The results obtained from the investigations were as follows: 1. Generally, the adult of striated chafer emerged from the middle of June to the middle of August. Especially, they emerged mostly in 1969, 1971, 1973 and 1975 in Loblolly pine stands of Shirahama. 2. In Kamigamo, six foreign pine-species were infested with the adult of striated chafer, P. banksiana, P. muricata, P. virginiana, P. pungens, P. rigida and P. echinata. Especially, the damages of P. muricata were severe. In Shirahama, there were P. elliottii, P. rigida and P. taeda. 3. The feeding amount of the adult of striated chafer was in proportion to these faeces during the same time, and the food consumption (F) was 1.143 times of the faeces (D) in the case of feeding of Loblolly pine needles. 4. The needles were cut down by the feeding behavior of the striated chafer, and these amount were estimated to be about 2.3 times of the food consumption on feeding of Loblolly pine needles (Fig. 1). 5. The body of the adult of striated chafer emerged in Loblolly pine of Shirahama was weighed mostly within the limits from 90 mg to 210 mg in dry weight (Fig. 3). 6. In Loblolly pine stands, the faeces of the adults of striated chafer weighed 10~26 kg per hectare in dry weight in 1969, 1971, 1973 and 1975 and 0.5~4.0 kg/ha in other years of investigated term. 7. Population of the adult of striated chafer in Loblolly pine stands was estimated early in July 2000 in 1972, 10400 in 1973, 2000 in 1974 and 13100 in 1975 per hectare by the faecal weight method (Fig. 6 and 7). 8. The annual loss of needles by grazing of the adult of striated chafer in Loblolly pine stands was estimated in maximum about 133 kg per hectare in dry weight (Table 4), accordingly it seemed that there were no damages in Loblolly pine stands.