天然林と人工林に人為的につけ加えられたマイマイガLymantria disparの死亡要因

概要

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The mortality factors of an experimentally established population were observed and analysed in order to elucidate the control factors which stabilize an insect population during periods of low density. The larvae of L.dispar were placed on birch trees (Betula ermanii var. communis) surrounded by one hectare unstocked space in a natural forest zone in Hokkaido, on larch trees (Larix leptolepis) which were planted in a natural forest, and on birch trees (B.platyphylla) in a 100 hectare larch plantation. The distance between the B.ermanii var. communis and L.leptolepis stands in the natural forest was about 100m, and 6km between the larch plantation and the natural forest. Although more than 90% of the larvae on B.ermanii var. communis or B.platyphylla were killed in one month from June to July, only about 65% of the larvae were killed on L.leptolepis in the natural forest. The larvae on the larch trees in the natural forest were not preyed upon by birds. The differences in mortality among the stands seemed to be caused mainly bird plundering. The Gordioidea parasite was found on about 20% of the larvae on the birch trees, but was not observed in other stands. All the stands were plagued by a species of dipterous parasite which caused high mortality and showed a tendency of density-dependency.
日本森林学会の論文
1975-12-25