PHYLLOPHAGOUS INSECTS IN STEPPE LARCH ...

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PHYLLOPHAGOUS INSECTS IN STEPPE LARCH FORESTS OF PRIOLKHONIE V.I. Epova Siberian Institute of Plant Physiology and Biochemistry, Russian Academy of Sciences, Siberian Branch, Irkutsk, Russia

Low heat provision of Priolkhonie, the arid climate and poor stony soils limit the distribution of wooden plants in the Tazheranskaya steppe. Drought resistance of the larch determines its monopoly on this territory. Thin, short larch forests of low quality index grow in the upper part of northern slopes. Herbage-grass, grass-herbage, shrub-herbage with Rhododendron, Spirea and Cotoneaster, Riihidia and stony larch forests are distributed here. Needle-biting insects play an important role in the steppe larch forests of Priolkhonie. Most phyllophagous insects mentioned are characterized by ecological plasticity. However, biotopical distribution of philophagous insects and the dynamics of their amount largely depend on microclimatic specificity of larch associations. Location of outbreaks of needle-biting insects (Erannis jacobsoni Djak., Orgyia antiqua L., Lymcintria dispar L.) to steppe larch forests is due to several reasons. Complete defoliation of trees results in the enhanced organic exchange what is important for tree life under steppe conditions. Physiological disturbance of metabolism in damaged trees is compensated in the following years after the damage, and the attack of the most weakened trees by trunk pests and their death is the result of natural selection. Ecological structuring of insect populations is linked with a discrete character of tree stand distribution in the steppe. Ecological and spatial components of the intrapopulational distribution determine genetic variability of philophages. The exchange of genetic information between intrapopulation groups is necessary to maintain the evolutional structure [Yablokov, 1987]. The efficiency of this process increases in the period of outbreaks. This is the only way to renew the genetic material in species with a limited migration activity (Erannis jacobsoni Djak., Orgyia antiqua L. ). Therefore, a periodic increase in the amount of particular intrapopulation groups is an evolutionary programmed phenomenon. Landscape and climatic peculiarities of the Tazheranskaya steppe contribute to realization of this programme. BIOCHEMICAL CHANGES IN NEEDLES OF LARIX SIBIRICA DAMAGED BY LARCH CASEBEARER (LEPIDOPTERA, COLEOPHORIDAE) I.Y. Ermolayev, M.V. Ermolayeva

V.N. Sukachev Institute of Forest, Russian Academy of Sciences, Siberian Branch, Krasnoyarsk, Russia

During 1996 analysis of nitrogen compounds, monosaccharides, and starch of Larix sibirica Ledeb. needles was performed. Plots were located in the forest- steppe larch forest partially defoliated by the larch casebearer Coleophora sibiricella Flkv. (Coleophoridae, Lepidoptera) in South Siberia at Kuznetsk Alatau intermountain area. We sampled ten larch trees with spring density of infestation of more than 1 larvae per brahiblast; 10 undamaged larches were taken as a control. Larch casebearer is a narrow oligophage on larches. It is noteworthy that even trees with maximum infestation are never completely defoliated and do not loose their resistance to xylophagous insect pests. The total and protein nitrogen content of damaged needles during the feeding period of the last instars caterpillars (June, 5) was found to be higher than that of the control ones (P